Document Kzz0Qb87648Mg9zJoBKNvrmZK

FILE NAME: Owens Illinois Library (OWL) DATE: 1951 DOC#: OWL030 DOCUMENT DESCRIPTION: Article from the Archives of Industrial Health Experimental Studies of Asbestosis i : A l9 ill A R C H I V E S OP Industrial Hygiene and Occupational Medicine EDITORIAL BOARD PHILIP DRINKER, Chief Editor 55 Shattuck Street, Boston 15 THEODORE F. HATCH, Pittsburgh FENN E. POOLE, Glendale, Calif. ROBERT A, KEHOE, Cincinnati FRANK PRINCI, Denver FRANK A. PATTY, Detroit WILLIAM A. SAWYER, Rochester, N. Y. JAMES H. STERNER, Rochester, N. Y. RICHARD J. PLUNKETT, M.D., Chicago, Managing Editor Volume 3 1951 PUBLISHERS AMERICAN MEDICAL ASSOCIATION CHICAGO 10, ILL. 10 Nose industrial perforated ulcers of septum In glass workers, 329 Nuclear Energy: See Radioactivity Occupations: See Industry and Occupations O'Connor, R. B. Analysis of existing types of small-plant health services In northeastern United States [O'Con nor], *73 Phlebitis abdominal anthracosilicotlc, 327 Phosphorus and Phosphorus Compounds phosphine poisoning, 421 phosphorus b u rn s: treatment, 437 Photofluorography: See Roentgen Rays Physicians viewpoint In Industry (Kessler], *185 workman and, 409 Odors control of, 217 Pittsburgh air pollution In [Ely], *44 O il: See also Castor Oil Bean derm atitis: from turpentine. 106 disposal: and varnish fume, 218 Osmium poisoning: by newer metals, 535 Otolaryngology Plantation medicine, 426 Plastics chlorovlnyl: conditions of work and Industrial hy giene measures in production of and manufacture from, 324 work placement of persons with diminished work ing capacity in, 324 Oxygen: See also Respiration atomic: at surface of freshly crushed silica. 414 Plotkin, T. Air flow measurements on human subjects with and without respiratory resistance a t several work rates, *461 inhalation o f: effects. 206 poisoning: In man, 32$ Paint Industry oil and varnish fumes: disposal, 218 Paints quick-drying: white blood cell counts of sprayers using: study of health of workers using benzene solvents In modem factory, 429 Pancreas lipocalc, histopathologic modifications in experi mental Intoxication due to trinitrotoluene, fol lowing therapy with methionine a n d : behavior of kidneys, adrenals, spleen, lungs and heart, 330 Faqutn, H. 0 ., Jr. Chronic toxicity of methylpolysiloxane "DC anti foam* A" in dogs, *479 Plutonium excretion and distribution of yttrium an d : effect of different dose levels of zirconium, 424 Pneumoconiosis advice to patients, 524 sbestosls: contribution to study, 428 asbestos!: experimental studies (Vorwald & oth ers], *1 cereal dusts: cause, 525 delayed. 418 emery dust: case due to, 525 in Germany, 419 kaolin: case attributed to, 529 mlneralogical aspects of research, 413 radiographic appearances*in coalminer's: classifica tion. 523 roentgen aspects of, 102 silicosis: acute, from ruck excavation, 105 Paralysis of respiration: first aid service for workers with, 537 Parathlon in air samples: determination by ultraviolet ab sorption spectroscopy, 431 anticholinesterase: activity in vitro of Insecticide, 327 toxic effects, 213 toxicology, 213 Peptic Ulcer cement: new occupational disease due to, 417 occupational facto rs: etiology, with estimate of their incidence In general population, 520 Periodicals Industrial Hygiene Newsletter renamed Industrial Health Monthly, 541 Transactions of Association of Industrial Medical Officers, 541 Petroleum cancer: environmental, and, 441 F rench: and Its possible use In prophylaxis of benzene poisoning, 329 leaded-petrol h andlers: paranoid states occurring til, 532 Petroleum Industry atmospheric contamination by petroleum-treating establishments, 433 personnel refining or selling: comparative study, 410 shale oil: hydrogen sulfide poisoning in [Ahiborg], 247 PG U P: See Propylene Glycol Dtproplonate Phenols In Blood: See under Blood silicosis: BCG vaccination in, 207 silicosis: Mood changes in slUcotuberculoals and, 418 silicosis: cardiorespiratory function In, test, 528 silicosis: compensation for change of employment in, 410 silicosis: electrocardiogram, significance, particu larly of chest wall leads, for evaluation of, 429 silicosis: erythrocyte sedimentation rate in stages of, 429 silicosis: freshly fractured surface, theory of, 208 silicosis: heart in, 530 silicosis medical bureau: Northern Rhodesia, 410 silicosis: In metallurglcsl Industry In France, 210 silicosis: among pottery workers In Limousin, 416 silicosis: problems, 417 silicosis: pulmonary bullous emphysema as cause of spontaneous pneumothorax in patients with. 527 silicosis: report on country-wide study In metal mines of Japan [Yamamoto], *339 silicosis: roentgenological evolution of asymptoma tic, 211 silicosis: In sand blasters, 210 silicosis: severe complicated, diagnosed 20 years after patient had left workplace In which there had been considerable dust exposure, 530 silicosis: suppression of dusts that may produce, 539 silicosis: temporary disability and. 417 silicosis: tuberculosis and dust, 419 silicotic lung: new' tests for study of, 209 \ silicotic lungs: freshly broken so-called old quartz from, comparative animal experiments on effect of, 423 Phenyl Mercury Compounds: See under Mercury Phenylalanine '5. >< ! . I n . f mnlt silicotic pneumoconioses: treatment of, 103 stllcotics: adrenocortical function tn, 320 MUcottcs vital capacity: Importance of methods Pneumoconiosis--Continued slllcottcs: vital capacity: mo< capacity and of other respirai pulmonary, 527 stannic oxide, 101 and 325 various form s: studied especial! pneumonoconlosls and baritot* sulfide, 526 Pneumonia metal dust pneumonitis, 211 Pneumothorax * spontaneous : pulmonary button cause In patients w ith slllcosi Poisons and Poisoning: See under ous substances, as Lead; etc. Polonium static elim inators: study of coi tlal of. 432 Polyneuritis : See Neuritis, multlp' Porphyrin and ro rp h y rtn Compoun In blood : Sec under Blood metabolism: adverse effect of B.' acute polyneuritis with observa Postman, B. F. Engineering control of occupatlo: 169 Pottery Industry silicosis among workers In L!m<> Pratt, P. C. Experimental studies of asbestos Prlckett, C. S. Occurrence of DDT In human f. Printing Industry benzene In : toxic effects, 425 Princl. F. Study o f workers exposed to lns< aldrtn, dleldrln, *64 Pritchard, ff. H. Five cases from fluorescent lamp ment of chronic beryllium pols and cortisone, *549 Propylene Glycol Dlproplonate toxicity o f (Ambrose], *48 Proteins requirement of h ard workers: 1> extractives on ability to work. Protoporphyrin: See Blood, porphyr compounds Psychiatry: See also Mental Dise viewpoint o f psychiatrist (in sol ards) (Bow m an], *181 Psychosomatic Factors in exhaustion of executives, 204 ru b llc H ealth : See also Hygiene Industry and Occupations atomic energy : aspects, 438 Quartz: See Pneumoconiosis; Sill Radiations: See also Roentgen Ra\ bibliography of detection, 115 gamma-ray dose : measurements radiotherapist during radium . hazards: In atomic energy progr injury: rases. In radiological w o. instruments for detection of rs; leukemia: in radiologists In 20 y< neutron cataracts, 412 photofluorographlc personnel : pr< problem of excessive: problem d restorations of heart, 115 "tolerance dose** for X and T r trial tolerance conference of ci. 439 vocational and atomic exposure l> 113 Radioactivity : See also Atomic Enctv Pneumoconiosis--Continued silicotics: vital capacity: modification of vital capacity and of other respiratory Indications In pulmonary, 527 stannic oxide, 101 and 325 various form s: studied especially In Ita ly : thlo- pneumonoconlosls and baritosis due to barium sulfide, 526 , . Fneumonla metal dust pneumonitis, 211 Pneumothorax spontaneous: pulmonary bullous emphysema as cause In patients with silicosis, 527 Poisons and Poisoning: See under names of poison* ous substances, as Lead; etc. Polonium static eliminators: study of contamination poten tial of, 432 Polyneuritis: See Neuritis, multiple Porphyrin and Porphyrin Compounds In blood: See under Blood . . metabolism: adverse effect of BAL In case acute polyneuritis with observations on, Postman, B. F. Engineering control of occupational health *169 Pottery Industry silicosis among workers in Limousin, 416 of sub 428 hazard, P ratt, P. C. Experimental studies of asbestosls, *1 Prickett, C. S. Occurrence of DDT in human fat and milk, *245 Printing Industry benzene in : toxic effects, 425 Prlncl, F. Study of workers exposed to insecticides chlordan, aldrin, dleldrln, *64 Pritchard, W. H. Five cases from fluorescent lamp industry: treat ment of chronic beryllium poisoning with ACTH and cortisone, *549 Propylene Glycol Dlproplonate toxicity of (Ambrose), *48 Proteins requirement of bard workers: influence of pure extractives on ability to work, 411 Protoporphyrin: See Blood, porphyrin and porphyrin compounds .Psychiatry:. See also Mental Diseases viewpoint of psychiatrist (In solving health hazards) [Bowman), *181 Psychosomatic Factors In exhaustion of executives, 264 'Public H ealth: See also Hygiene and Sanitation: Industry and Occupations atomic energy: aspects, 438 Quartz: See Pneumoconiosis; Silicon Compounds Radiations: See also Roentgen Rays bibliography of detection, 115 gamma-ray dose: measurements of, received by radiotherapist during radium operations, 222 hazard s: in atomic energy program, control, 439 Injury: cases, In radiological work, 223 Instruments for detection of rays. 114 leukem ia: In radiologists In 20 year period, 222 neutron cataracts, 412 photofluorographlc personnel: protection of, 114 . problem of excessive: problem during routine In vestigations of heart, 115 "tolerance dose" for X and T radiation: Indus trial tolerance conference of currently accepted, 439 vocational and atomic exposure burns: treatment, 113 x . Radioactivity: See also Atomic Energy: Radiations: Radioactivity--Continued blood changes: in lumtnlzers using material, 441 isotope: appraisal of detergency through, 546 isotope: planning small program, 539 Isotope: radiation-exposure purvey of x-ray and. personnel, 446 isotope studies In experimental animals, small selfcontained laboratory for [Sognnaes 4 Shaw), *316 monel metal nasopharyngeal radium applicator: exposure of personnel handling. 113 static eliminators: hazards from, 112 substances In biological tissues, 115 unite of, 114 waste disposal, 113 Radioisotope: See under Radioactivity Radium : See also Radiations; Radioactivity in exposed humans: direct method for determining. 446 Read,' H. Viewpoint of union (toward plant industrial health program), *188 Rehabilitation physical medicine and, therapy of hand [Flax], *236 vocational: of psychiatric patients, 215 Injuries Retndollar, W. F. Health and atr pollution, *399 Religion viewpoint toward plant health program (Henry], 192 Renner, W. F. Significance of exercise tolerance test. *129 Respiration air flow: measurements on human subjects with and without respiratory resistance at several work rates [Silverman 4 others], *461 artificial: new method and comparative study of different methods In adults, 428 cardiorespiratory function In silicosis: test, 528 paralysis o f: first aid service for workers with. 337 vital capacity of silicotics: Importance of methods of determining theoretical vital capacity of sili cosis, 527 ( vital capacity of silicotics: modification of vital capacity and of other respiratory indications in pulmonary silicosis, 527 Respiratory T ract: See Nasopharynx; Nose: etc. Reynolds. P. \V. Beryllium disease from ceramic Industry: report of case, *575 Rheumatism work placement: of persons with diminished capac ity due to, 324 Roentgen Rays: See also Radiations aspects of anthracoslUcosls, 162 biological significance of, 222 diffraction method for finding quartz In Industrial dusts [Schmelzer], *121 exposure survey of Isotope and, personnel. 446 personnel monitoring, 441 roentgenological evolution of asymptomatic sili cosis, 211 workers: positive cephalin-cholesterol flocculation test in, 438 Safety m ine: t achievements, research and problems yet to be solved, 336 mine: research, twenty-seventh report, 1948. Lon don, 219 J In water and sewage works, problems of industrial hygiene and, 332 Sandblasting Industry silicosis :t in sand blasters, 216 Sander. O. A. r h r m t l o bcrvlllo!* In in*'* h!-; Int i-trv . **it* 428 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE ABSTRACTS A rtificial R espiration : A N ew Method and a Comparative S tudy of D ifferent Methods which asbestosis appeared, it w; in A dults. A. S. Gordon, D. C. Faiver and A. C. Ivy, J. A. M. A. 144:1455-1464 (Dec. asbestosis rather than to the ord 23) 1950. genologic examinations indicate tl The relative efficiency of the pulmonary ventilation obtained by manual and by mechanical methods of artificial respiration was studied on 109 warm corpses and nine normal subjects. The manual techniques utilizing both "push and pull" principles provided about twice the minute volume obtained with only a "push" or a "pull" method. The "push and pull" techniques ) these miners it develops so slov that it predisposes to tubercolosi' j j of experts from Saranac. 1 include the Nielsen (armlift-scapular pressure), the Schafer-Emerson-Ivy (hiplift-prone pres sure and hiproll-prone pressure) and the Schaffer-Neilsen-Drinker (armlift-prone pressure) T h e E rythrocyte S edimentati , Fay, Rev. Md. Minire, 195 methods. The simple "pull" methods of hiplifting or rolling are more effective than the "push" method of Schaffer. These procedures are compared as to ease of execution. Using the Fuente Hita methorate in 464 cases of silicosis. Tl In addition, the adequate mechanical methods of intermittent positive devices and alternating subjects for several years. In 30 positive and negative pressure resuscitators are discussed and compared with manual pro rated sedimentation rate, which n cedures in regard to efficacy and relative merits. The mechanical techniques have the advantages 84 of 108 cases of the nodular ty of simplicity of proper administration, being non-fatiguing, and of supplying 100 per cent oxygen, (90) they observed two types of and they may be used when patients cannot be moved because of the nature of the injury. ; in those with shadows showing re The chief advantage of the manual techniques is the equally effective pulmonary ventilation were produced as in the precedin' without need of. special equipment. A rnold a ^ BostolL The authors believe the erythroi A n A dverse E ffect of B A I. in a Case of S ubacute P olyneuritis with O bservations on of silicosis. Porphyrin M etabolism. James H. Sands, B arnet B erris and L. R aymond S cherer, New England J. Med. 248:558-561 (Oct. 12) 1950. I S ignificance of t h e E lectrocai ation of S ilicosis. J. Ho, A case of arsenical polyneuritis treated with dimercaprol (BAL, British antilewisite) is pre sented. Marked aggravation of neurologic symptoms and signs followed the administration of dimercaprol in the usual dosage. This is believed to be the first report of such an adverse response to dimercaprol during treatment of arsenical poisoning. Possible explanations are considered. Serial urinary arsenic and coproporphyrin studies are described. The urinary type III copro porphyrin excretion was markedly elevated, and the erythrocyte protoporphyrin considerably f elevated. Dimercaprol therapy caused a slight increase in the urinary excretion of arsenic and coproporphyrin, although the findings were not conclusive. According to the German law be granted in cases of pneumor provided that "the coniotic new reduced respiratory capacity an capacity of the body becomes cc patient with silicosis and reduce reaction may be determined ear decompensation has not yet rest: A daptation of A uthors' S ummary. It also facilitates differentiation o Electrocardiographic records W ork Evaluation of Rehabilitation. A. L. Stevens, Occup. Therapy 29:157 (June) 1950. chest wall electrocardiograms a differentiation of myocardial les- A Contribution to the Study of Asbestosis. P. Cartier, Arch, malad. profess. 10:589-595, may be demonstrated with their 1949. by the extremity-electrocardiogra'- For more than three years the author has been in medical charge of 3,242 men employed in mining asbestos at Thetford in Canada. At these mines over 70 per cent of the world's supply of asbestos is obtained. Forty per cent of the men have been employed for 10 to 40 years. The minerals mined consist of asbestos in the form of chrysolite and serpentine. Dust from serpentine lias been found clinically and by experiment to be a nuisance rather than a source of pneumoconiosis. But it is known that asbestos originates asbestosis, at least when its dust is generated while the mineral is being spun and woven into cloth. Cases of asbestosis were found only in those who had been employed for at least 14 years and exposed to air containing 5,000,000 or more particles of asbestos fibers per cubic foot, the fibers being from 10 to 250 microns in length. The outstanding feature of this report is the mildness of any pulmonary trouble found among the miners resulting from inhalation of asbestos dust, compared t \ ! ! ! aid in the diagnosis of the lex and the left ventricle, respective, of an increased hemodynamic b; as a "circulatory reaction" in t'. majority of cases without any <' Myocardial lesions were deni patients, and five of the 27 pi Localization of the myocardial h the chest wall electrocardiogram instances. Extrasystoles, arrhyt addition to changes in the ST se with what has been reported in the United States and Great Britain as occurring in factories where asbestos is spun and woven. Clinically none of the symptoms of pulmonary fibrosis-- cough, dyspnea, cyanosis and loss of weight--were present. No case of pure asbestosis was detected in those under age 60, and most of them were carrying on their work without any \ W hite B lood Cell Counts or H ealth of W orkers U s r i and K. T- V esel, Casopis physical incapacity. The mining neighborhood would seem to be unduly "infected" with tubercu V ' Blood examinations were carrn losis, but cases of that disease were not found to be any more frequent among the miners than quick-drying paint which was diss A B STR A C T S FROM CI URRENT L ITE R A TU R E which asbestosis appeared, it was difficult to ascribe any cardiac affections present1to the asbestosis rather than to the ordinary wear and tear of life. Postmortem findings and roent genologic examinations indicate that asbestosis is undoubtedly a pathological entity; .but among these miners it develops so slowly as not to shorten working life, and there is no evidence that it predisposes to tuberculosis. The conclusions arrived at are supported by the opinions of experts from Saranac. E. L. CoLLIS [Bull H yg.]. T he E rythrocyte S edimentation Rate in Stages of Silicosis. F . F oubert and G, L a Fay, Rev. Md. Minire, 1950, nos. 9 and 10, p, 19. Using the Fuente Hita method in a sloping tube, the authors have studied the sedimentation rate in 464 cases of silicosis. They have established sedimentation curves after observing the subjects for several years. In 30 cases of silicotuberculosis they almost always found an accele rated sedimentation rate, which might precede the manifestation of the tuberculous process. In 84 of 108 cases of the nodular type, they observed a low rate. In cases with massive shadows (90) they observed two types of curve, high in cases with diffuse extensive shadows and low in those with shadows showing retraction. ' In 236 cases with coalescent shadows the same results were produced as in the preceding category, according to whether they were progressive or not. The authors believe the erythrocyte sedimentation rate to be useful in following the progress of silicosis. E nglish S ummary. S ignificance of the E lectrocardiogram, Particularly of Chest W all L eads, for Evalu ation of S ilicosis. J. H ormann, Ztschr. Kreislaufforsch. 39:624 (O ct) 1950. According to the German law of compensation for occupational diseases, compensation must be granted in cases of pneumonoconiosis associated with progressive pulmonary tuberculosis, provided that "the coniotic new growth of connective tissue within the lung tissue causes reduced respiratory capacity and circulatory reaction to such an extent that the functional capacity of the body becomes considerably impaired." Fair evaluation of the condition of the patient with silicosis and reduced functional capacity, therefore, requires that any circulatory reaction may be determined early. Observation of this circulatory reaction, particularly if decompensation has not yet resulted, may be obtained with the aid of the electrocardiogram. It also facilitates differentiation of myocardial lesions due to silicosis and those of other origin. Electrocardiographic records obtained from 107 patients with silicosis demonstrated that chest wall electrocardiograms are most useful with regard to both circulatory reaction and differentiation of myocardial lesions, because changes in the ST segment and in the T waves may be demonstrated with their aid at a time when those changes cannot yet be demonstrated by the extremity-electrocardiograms. The chest wall electrocardiograms are also of considerable aid in the diagnosis of the localization of the objectivated myocardial lesions of the right and the left ventricle, respectively. The occurrence of typical steep curves as a manifestation of an increased hemodynamic burden placed on the right ventricle may ndt yet be considered as a "circulatory reaction" in the legal sense, since a typical steep curve occurs in the large majority of cases without any clinical symptom of impairment of the heart. Myocardial lesions were demonstrated on electrocardiographic examination in 27 of the 107 patients, and five of the 27 presented a normal curve in the extremity-electrocardiogram. Localization of the myocardial lesions in the left ventricle could be diagnosed with the aid of the chest wall electrocardiogram in 11 instances, and localization in the right ventricle in nine instances. Extrasystoles, arrhythmias and one typical Wilson block could be demonstrated in addition to changes in the ST segment in the remaining pathologic electrocardiographic records. W hite B lood Cell Counts of S prayers U sing Q uick-D rying P a in t s : A Study of t h e H ealth of W orkers U sing B enzene Solvents in a Modern F actory. F. J indrAk , and K. T. V esel^, Casopis L6karu Ceskych 89:285-288 (March 10) 1950. 1Blood examinations were carried out for 25 persons employed as many as 23 years in spraying quick-drying paint which was dissolved in solvents of the benzene type. Spraying was carried M ites Volume 3 Al al Industrial Hygiene and Occupational JANUARY 1951 Copyright, 1951, by t h e American Medical Association Medicine N umber 1 EXPERIMENTAL STUDIES OF ASBESTOSIS ARTHUR J. VORWALD, Ph.D.lPoth.), M.D. THOM AS M. DURKAN AND PHILIP C . PRATT, M.D. SARANAC LAKE, N. Y. ASBESTOSIS is a form of pneumonoconiosis resulting front pro^ longed inhalation of asbestos dust. The name "asbestos," literally "unburnable," is not that of a specific mineral but is a term applied to a number of different minerals whose characteristic feature is a structure composed of long, parallel, flexible fibers. This structure is unique because the fibers are capable of repeated longitudinal subdivision to units of molecular proportions. In length the fibers vary from a few microns to 6 or more inches (15 or more cm.). Some varieties are stiffer than others, but many are sufficiently flexible to be spun into yarn and woven on modified textile machinery. The asbestos minerals are silicates of variable composition and belong to the serpentine and the amphibole groups. Listed below are the more common varieties. Amphibole group: actinolite, amosite, amphibole, anthophyllite, crocidolite and tremolite. Serpentine group: chrysotile. The bulk of the asbestos of commerce is chrysotile, 3M g0.2Si0,.2H ,,0, which is mined on this continent principally in the Thetford region of the Province of Quebec, Canada, and in Vermont. Crocidolite and amosite also are used commercially but in much smaller amounts. Chrysotile occurs as veins in serpentine, a mineral of similar chemical composition, which exists in massive form and is made up of microscopic fibers without the parallel orientation characteristic of chrysotile. The massive, bluish black serpentine, which is smooth and soapy to the touch, is traversed by veins of fibrous chrysotile varying in width from a barely perceptible line to 6 (15 cm.) or more inches. The fibers run across the vein and not lengthwise with the formation. From the Saranac Laboratory of the Edward L. Trudeau Foundation. This series of studies of asbestosis, initiated at the Saranac Laboratory more than twenty years ago by the late Dr. Leroy U. Gardner, director of the laboratory, was nearly completed at the time of his death in October 1946. Although partial reports and informal reviews of some of the experiments had W n f- ' vi CONTENTS OF VOLUME 3 JUNE-- C ontinued PAGE Chronic Beryllium Poisoning of Long Duration from Fluorescent Lamp Manufacturing: Report of a Case. George K. Fenn, M.D., Beverly, Mass.............................................. 571 Beryllium Disease from the Ceramic Industry: Report of a Case. Preston W. Reynolds, M.D., Schenectady, N. Y................................................................................................. 575 Metabolic Study of a Oise of Chronic Beryllium Poisoning Treated with ACTH. Harriet L. Hardy, M.D.; Frederic C Bartter, M.D., Boston, and Abraham E. Jaffin, M.D., Jersey City, N. J .............................................................................................................. 579 Choice of Drugs and Dosage. Howard S. Van Ordstrand, Cleveland.......................... . 583 Recognition and Prevention of the Complications of ACTH and Cortisone Therapy. Thomas F. Frawley, M.D., Boston............................................................................................... 587 Information Gained in Pretherapy and Post-Therapy Pulmonary Function Studies. John McClement, M.D, New York.......................................................................................... 599 Pulmonary Function in Patients with Pulmonary Disease Treated with ACTH. B. G. Ferris Jr., M.D.; J. E. Affeldt, M.D.; H. A. Kriete, A.B., and J. L. Whittenberger, M.D., Boston ................................................................................ 603 Interpretation of Results of ACTH and Cortisone Therapy in Chronic Beryllium Poison ing : Data Obtained by Pretherapy and Post-Therapy Studies of Pulmonary Function. George W. Wright, M.D., Trudeau, N. Y...................................................................... 617 Minimum Observations Necessary to Advance Knowledge of the Action of ACTH and Cortisone. Anne Forbes, M.D., Boston............................................................................ 622 Current Research Problems Concerning Pulmonary Granulomatosis in Beryllium Work ers. Friedrich Klemperer, M.D., Trudeau, N. Y.............................................................. 625 General Discussion on the Treatment of Chronic Beryllium Poisoning with ACTH and Cortisone ........................................................................................................................... 629 Health Hazards in the Production and Handling of Vanadium Pentoxide. Sven-Gosta Sjberg, M.D., Eskilstuna, Sweden................................................................................. 631 News and Comment.................................................... 647 Book Reviews .......................................................................................................................... 648 M ires Vo lu m e 3 A. ni Industriai H) JA N Co py r ig h t , 1951, b y t i EXPERIMENTAL ` ARTHUR . VO. THOMa PHILIP SARAN A S B E S T O S IS is a form oi -a x longed inhalation of asbest "unbum able," is not th at of a sj num ber of different m inerals w! composed of long, parallel, fle> because the fibers are capable units of molecular proportions, microns to 6 or more inches ( stiffer than others, but many a: yam and woven on modified tt T he asbestos minerals are silk to the serpentine and the amphib common varieties. Amphibole group: actinolite crocidolite and tremolite. Serpentine group: chrysotile. T he bulk of the asbestos of c 2H .O , which is mined on this eont; of the Province of Quebec, Can: amosite also are used commerci Chrysotile occurs as veins in se r composition, which exists in massiv fibers w ithout the parallel orienta massive, bluish black serpentine, w is traversed by veins of fibrous barely perceptible line to 6 (15 c across the vein and not lengthwis From the Saranac Laboratory of t This series of studies of asbestosis. than twenty years ago by the late Dr. Lt was nearly completed at the time of hi.reports and inform al review. of some of ' 2 INDUSTRIAL HYGIENE AND. OCCUPATIONAL MEDICINE Attention is directed to the mineral brucite, MgO.HX), which is often found in the same formations with serpentine and chrysotile and may be fibrous in structure. Except for the manufacture of magnesium, brucite lias no commercial value at present because its fibers are not sufficiently flexible to be used in textiles, but they are capable of repeated longitudinal subdivision. Unlike other asbestiform minerals, brucite is not a silicate, and for this reason it has been a valuable tool in an experimental evaluation of the action of fibrous minerals on lung tissue. experimental asbestosis For many years studies1 have been carried on at the Saranac Laboratory in an investigation of the cause, nature and development of asbestosis. The present paper is devoted to experimental asbestosis, Fig. 1.--Human asbestosis (P-36-144). The photomicrograph reveals a bronchi ole (right center) with a smooth muscle bundle at its inferior margin and with an extensive zone of collagen deposition largely obliterating the surrounding alveolar structure. The black foci are macrophages containing incidental pigment. Asbestosis bodies are present but are not apparent at this magnification (X 200). and in it are described the experiments made on animals with various kinds of asbestos dust. Another report, to be prepared and issued at a future date, will be concerned with human asbestosis and will cover the health aspects of workers who have been exposed to asbestos dust in an industrial environment. Although in man asbestosis is a chronic disease with diffuse pulmo nary fibrosis which requires years to develop, it is possible to reproduce 1. (a) Gardner, L. U., and Cummings, D. E.: Studies on Experimental Pneumokoniosis: VI. Inhalation of Asbestos Dust; Its Effect upon Primary Tuberculous Infection, J. Indust. Hyg. 13:65 and 97, 1931. (b) Gardner, L. U .: Chrysotile Asbestos as an Indicator of Subtile Differences in Animal Tissues, Am. Rev. Tiilmrr 4S r7A? 104> I VORWALD ET A L --S " in one or more, species of animal c similar to the lesions of human asb< the experimental animal is relative the characteristic lesions in animal usual industrial environment. Coi ation of the tissue response to inh it is necessary to accelerate the r a tions of dust than would ordinaril conditions of exposure are thus < animal experiments is invaluable it the reaction of the human organist E xperimen F or investigating the tissue rea various asbestos minerals, two ty namely, the inhalation method am experiments, groups of animals-- sometimes smaller numbers of r; kept for eight hours a day in a < dimension, in which a cloud of asb paddle in a dust hopper.1* At inanimals are killed and the tissues and the extent of the dust reacti periods up to three years. The inj mine in as short a time as possible a potential capacity to produce ir contact with tissues of the body, dust, either dry or suspended in flui the intraperitoneal, the intratrachea Long term inhalation experim great reliance is placed when estimaconstitute a respiratory hazard to i atmospheric dust may be potential!} experiments, only inhalation proced lie inhaled, pass the natural defens pulmonary tissue in quantities suP methods are useful, however, bee: occurs between the dust particles accurate estimation of the dosage ; dose to produce reaction. The i valuable when one is dealing with it permits observation of the effect o` T ssue Si Unlike free silica, asbestos doc organs of all species of animats, table 1 are based on completed obse  L L bt1ALIGN AL MEDICINE of various animals (guinea pig, rabbit, rat, mouse, cat, dog, chicken and even tadpole) eventually will produce silicotic nodules but at different rates. Similar introduction of long fiber asbestos has resulted in a fibrous reaction in the lung and, to a lesser extent, in the peritoneum but not in other organs of the guinea pig, the rabbit, the cat and the white rat. In our experience the lungs of the dog and the white mouse failed to respond with fibrosis, although Schuster 2 has reported such changes in a dog that lived in an asbestos-fabricating plant. This variation in species and in organ susceptibility is yet to be accounted fo r3; it is presumed that in the susceptible animals the greater reaction of the lung to asbestos, far exceeding the reaction of other organ tissues, is due principally to the greater mobility of the lung. P eculiar C haracteristics of A sbestos Experience has demonstrated that most of the nonfibrous dust particles inhaled into the lungs of man and animal are 10 microns or less T able 1.--Reaction io Long Fiber Chrysolite in Lungs of Man and Other Species of Animal \ Species Mao....................... Guinea pig............. Rabbit................... C at........................ White rn t.............. White mouse......... Dog.................... . Mode ot Exposure Inhalation Inhalation and injection Inhalation and Injection Inhalation and Injection Inhalation and injection Inhalation Injection Fibrosis * 4+ 2-1+ -i+ 0 0 Asbestosls Bodies Numerous Moderately numerous Rare and atypical Rare and atypical Very rare Rare and atypical None * The symbols 0 to 4+ reler to the degree of tissue reaction. in maximum dimension. Larger particles apparently do not gain access to the lungs, because, first, large particles settle in air so rapidly that few remain suspended in the atmosphere breathed and, second, large particles are more effectively removed by the protective mechanisms of the upper respiratory tract. In the case of fibrous materials these factors have less influence and fibers 100 and even 200 microns in length have been found in the terminal air spaces of human lungs. In small labora tory animals exposed to asbestos dust the maximum length of fiber found in the lung rarely exceeds 60 microns. A large proportion of nonfibrous particulate dust inhaled into the lung is found in the terminal air spaces (alveolar ducts, atriums, alveoli) in all parts of the organ; in contrast, inhaled asbestos fibers are first discovered in the respiratory bronchioles. These small passages are immediately distal to bronchioles lined bv ciliated epithelium.4 Their 2. Schuster, N. H .: Pulmonary Asbestosis in a Dog, J. Path. & Bact. 34 (pt. 2):751, 1931. ' 3. Vorwald, A. J . : Variations in Individual Susceptibility to Industrial Dusts Inhaled into the Lungs, Am. Rev. Tuberc. 62: (IB) 13, 1950. 4. Miller, W. S .: The Lung, Springfield, 111., Charles' C Thomas, Publisher, 1937. VORWALD L own essential lining is ; name implies, they act alveoli distributed along change in the character of the respiratory bronc' responsible for retention is well established are a; peripheral air spaces. 1 observation. R ate of T i The affected tissues quartz dust. For exantj tracheal injection fibrosis one month after injection months or more. Thus, inhaled silica lags behind ; does the evolution of the < difference in the degree exposure to dust. For > nodules of silicosis become period of time, whereas t' short time. Subsequently, process often distorts the a< progressively interfere with The peculiar structure body" is a specific concern golden yellow, beaded or h; or curved (fig. 2 ). Often o. The bodies vary considera. microns have been recorded It is believed that asbest tein and iron pigment of tis observed reproduction of the sulicutaneous injection of fil abundant in man and in the in the former, probably bo fibers of greater dimension. 5. Gloyne. S. R .: (a) The : Tubercle 12:398, 1931; (b) The . ner and Cummings.1" 6. Lynch, K. M., and Smith, J. A. M. A. 9S:659 (Aug. 30) Asbestosis Bodies in the Sputum : Asbestos Mill, J. Path. & Bact. 34 filoviie.5a- b VORWALD ET AL.--STUDIES OF ASBEST0S1S 3 in one or more, species .of animal characteristic tissue changes which are similar to the lesions of human asbestosis (fig. 1). Since the life spart of the experimental animal is relatively short, it is not possible to produce the characteristic lesions in animals under conditions identical with the usual industrial environment. Consequently, to obtain a complete evalu ation of the tissue response to inhaled particulate and fibrous material, it is necessary to accelerate the reaction by employing higher concentra tions of dust than would ordinarily be encountered in industry. While conditions of exposure are thus different, the information yielded by animal experiments is invaluable in furnishing a better understanding of the reaction of the human organism to inhaled asbestos dust. E xperimental Methods For investigating the tissue reactions of experimental animals to the various asbestos minerals, two types of technic have been employed, namely, the inhalation method and the injection method. In inhalation experiments, groups of animals--up to 100 or more guinea pigs and sometimes smaller numbers of rabbits, cats, dogs, rats or mice--are kept for eight hours a day in a cubical dust room, 8 ft. (2.5 M.) in dimension, in which a cloud of asbestos dust is maintained by a rotating paddle in a dust hopper.1" At intervals during the experiment a few animals are killed and the tissues examined to determine the nature and the extent of the dust reaction. Some animals are exposed for periods up to three years. The injection experiments are used to deter mine in as short a' time as possible whether or not a particular dust has a potential capacity to produce inflammatory reaction when in direct contact with tissues of the body. The method involves injecting the dust, either dry or suspended in fluid, into the animal by the intravenous, the intraperitoneal, the intratracheal or another route. Long term inhalation experiments furnish information on which great reliance is placed when estimating the degree to which a dust might constitute a respiratory hazard to industrial workers. Even though an atmospheric dust may be potentially dangerous, as indicated by injection experiments, only inhalation procedures will reveal whether the dust can be inhaled, pass the natural defense barriers of the body and reach the pulmonary tissue in quantities sufficient to cause damage. Injection methods are useful, however, because they make certain that contact occurs between the dust particles and tissues and because they allow accurate estimation of the dosage and of the potential capacity of that dose to produce reaction. The intratracheal method is particularly valuable when one is dealing with fibrous minerals like asbestos, since it permits observation of the effect of the fibers on pulmonary tissue. T issue S usceptibility Unlike free silica, asbestos does not produce specific effects in all organs of all species of animals. The comparative data presented in table 1 are based on completed observations and therefore differ slightlv VORWALD ET AL.--STUDIES OF ASBESTOSIS 5 own essential lining is a low cuboidal type of epithelium but, as their n am e`implies, they actually function in respiration through lateral alveoli distributed along their walls. Either these alveoli or the abrupt change in the character of the lining epithelium, or the small diameter of the respiratory bronchiole, or the combination of all three factors is responsible for retention of the fiber at this site. Only after asbestosis is well established are appreciable numbers of fibers seen in the more peripheral air spaces. Further explanation is required to clarify this observation. R ate of T issue R eaction to A sbestos F ibers The affected tissues react much- more rapidly to asbestos than to quartz dust. For example, in ratsireceiving asbestos fibers by intra tracheal injection fibrosis of a characteristic type is visible as early as one month after injection; for quartz dust the latent period is two months or more. Thus, the development of nodular fibrosis due to inhaled silica lags behind the deposition of dust to a greater extent than does the evolution of the diffuse reaction to asbestos. This results in a difference in the degree of progression which follows termination of exposure to dust. For example, on discontinuance of exposure the nodules of silicosis become larger, to a limited extent, for a considerable period of time, whereas the fibrosis of asbestosis increases for only a short time. Subsequently, the asbestotic fibrous tissue contracts; this process often distorts the adjacent pulmonary tissue and may, as a result, progressively interfere with cardiorespiratory function. A sbestosis Bodif.s The peculiar structure known as the asbestosis body or "curious body" is a specific concomitant of asbestosis.56 The typical body is a golden yellow, beaded or haustrated rod, which may be either straight or curved (fig. 2). Often one or both ends are bulbous like a dumbbell. The bodies vary considerably in length, and dimensions up to 250 microns have been recorded. It is believed that asbestosis bodies are inhaled fibers on which pro tein and iron pigment of tissue origin have been deposited.* Gloyne5b observed reproduction of these bodies in guinea pigs nine months after sulxrutaneous injection of fibers rendered free of iron. The bodies are abundant in man and in the guinea pig (table 1) but are much larger in the former, probably because the larger-sized air passages admit fibers of greater dimension. In guinea pigs they form after about 70 days 5. Gloyne. S. R .: (a) The Formation of the Asbestosis Body in the Lung, Tubercle 12:398, 1931; (b) The Asbestosis Body, Lancet 1:1351, 1932. (r) Gard ner and Cummings.'" 6. Lynch, K. M., and Smith, W. A .: Asbestosis Bodies in Sputum and Lung, J. A. M. A. 95:659 (Aug. 30) 1930. Simson, F. W., and Strachan, A. S .: Asbestosis Bodies in the Sputum: A Study of Specimens from 50 Workers in an Asbestos Mill, J. Path. & Bact. 34:1, 1931. Gardner and Cummings.'" Gardner Glovne.""" *> 6 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE of contact with the tissue. In cats, rabbits and mice a few of the fibers show an atypical coating after much longer residence in the lungs. In rats the bodies are rarely seen, and in dogs none could be found. Although the evidence is incomplete, it appears that the formation of the asbestosis body prevents the fiber from damaging the tissue. Many of the points mentioned above will be elaborated on in subsequent para- Fig. 2.--A , human asbestosis bodies. This collection of asbestosis bodies was found in the lung shown in figure 1. The usual variations of size and configuration are represented ( x 400). B, guinea pig asbestosis body. This one is similar to some of those shown in A (X400). i graphs dealing with the actual experiments. For presentation our ......... rK.-wWI .-r-r'iirmc ntv> rlnnlimr yvitli inbnlntion VORWALD E T A L.-. INHALATK Four large scale inhalation e: laboratory with various forms of gtions, more than 160 animals carried on for periods ranging f; four kinds of asbestos dust eni* short fiber, 100 per cent ball-mi K ing's F lo.\ T he first inhalation experime: with asbestos dust was begun ii T able 2.-- Chemical Anah Type of Asbestos King's floats............. Short fiber............. .. Long fiber............. .. SIOs 39.32 37.17 38.40 FesOa AlsOt CfsO: s-- "' "V 9.00 1.40 0.14 5.32 0.78 * Not determined. T able 3.--Petrographic Ana King's Rosts *: The approximate eomp> than 10 microns and reported as percents? serpentine 40, magnetite 12, carbonates is, t 200 microns long were included. Short fiber t: The material, before bell chrysolite and piaty (nonflbrous) serpentine chrysotile 17, serpentine 55, magnetite 10, qi aetinolite and tremolite, 11. Long fiber t: The m aterial consisted v Shreds of nonseparated fibers S to IS micro present. The approximate composition, by netite 5, brueite 2, other minerals, amom minerals, 3. Only a traee of quartz was ot T h e analysis of the King's floats asL University, has been reported elsewhere (li eralogy of Asbestos Dust, 3. Indust. Hyg. t For the short fiber asbestos and the supplemented with x-ray diffraction examh; periods up to 33 months. Some exposure lived for an addition: exposure. A preliminary repor months of exposure. A t that tin' 2)4 years and the conclusions : asbestos dust were provisional, results of the completed study, w Composition and Atmospheric Cone a commercial variety of asbestos kn<c fibers, ranging in length from 1 mm. also varied in size. It was obtainc Asbestos Corporation of America, an ... . ..... r ci....... ,.i.... VORWALD E T AL.--STUDIES OF ASBESTOSIS 7 INHALATION EXPERIMENTS F our large scale inhalation experim ents have been conducted in this* laboratory with various forms of asbestos dust. In each of these investi gations, more than 160 animals were used, and the experiments were carried on for periods ranging from two to more than five years. T he four kinds of asbestos dust em ployed are designated as K ing's floats, short fiber, 100 per cent ball-milled, and long fiber asbestos dust. K ing's F loats A sbestos D ust T he first inhalation experiment conducted at the Saranac Laboratory with asbestos dust was begun in 1928. Animals inhaled the dust for T able 2.--Chemical Analysis of Asbestos Dusting Materials Type of Asbesto imi* faon SIO* FesOs AlsOi Cr+Ot MoO CaO MgO N a-0 K -0 CO* Loss Total Kind's floats............. 39.32 8.8* * * 0.67 &V.VJ * 12.74 07.13 Short aber................. 37.17 9.00 1.40 0.14 0.09 0.85 35.96 0.14 0.20 0.98 14.00 100.11 Long fiber................. 38.40 5.32 0.78 * 0.08 0.31 40.18 0.06 0.06 0.57 14.00 99.76 * Not determined. T able 3.--Petrographic Analysts of Asbestos Dusting Materials King's floats *: The approximate composition, based on particles (except chrysotlle) smaller than 10 microns and reported as percentages obtained from particle counts, was chrysotlle 14, serpentine 40. magnetite 12, carbonates 18, talc 12, other minerals 4. For chrysotlle, fibers up to 200 microns long were Included. Short fiber t: The material, before being ball milled, contained a preponderance of fibrous chrysotlle and platy (nonflbrous) serpentine. The approximate composition, by percentage, was chrysotlle 17, serpentine 55, magnetite 10, quartz 2, brucite 6, other minerals, including dolomite, actinollte and tremolite, 11. Long fiber t: The material consisted principally of the fibrous asbestos mineral chrysotlle. Shreds of nonseparated fibers 5 to 15 microns in diameter and up to 50 microns in length were present. The approximate composition, by percentage, was chrysotlle 75, serpentine 15, mag* netite 5, brucite 2, other minerals, among which were calcite and chloritic and micaceous minerals, 3. Only a trace of quartz was observed. * The analysis of the King's floats asbestos, made by Dr. C. S. Iluribut Jr., of H arvard University, has been reported elsewhere (Hurlbut. C. S., Jr., and Williams, C. R.: The Min* eraloiry o f Asbestos Dust, J. Indust. Hyg. k Toxicol. 17: 292, 1935). t For the short fiber asbestos and the long fiber asbestos the petrographic analysis was supplemented with x-ray diffraction examination. periods up to 33 months. Som e guinea pigs with six and nine m onths' exposure lived for an additional three years after cessation of their exposure. A preliminary r e p o r t1B presented observations after 29 months of exposure. At that time observations covered a period of only 2'A years and the conclusions as to the ultimate effects of inhaled asbestos (lust were provisional. T hose conclusions are substantiated by results of the completed study, which is reported as follows. Composition ami Atmospheric Concentration of the Dust.--The dusting material, * a commercial variety of asbestos known as King's floats, was composed of short fibers, ranging in length from l mm. to l micron or less, and of particles which also , varied in size. It was obtained from the Thetford, Quebec, plant of the Asbestos Corporation of America, and analyses (tables 2 and 3) reveal that the ..........* f ci... ... . i.,-.-. ,-.n1v 14 nor rent, a rather low value. 6 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE of contact with the tissue. In cats, rabbits and mice a few of the fibers show an atypical coating after much longer residence in the lungs. In rats the bodies are rarely seen, and in dogs none could be found. Although the evidence is incomplete, it appears that the formation of the asbestosis body prevents the fiber from damaging the tissue. Many of the points mentioned above will be elaborated on in subsequent para- Fig. 2.--A , human asbestosis bodies. This collection o{ asbestosis bodies was found in the lung shown in figure 1. The usual variations of size and configuration are represented (X 400). > B, guinea pig asbestosis body. This one is similar to 7some of those shown in A (X 400). graphs dealing with the actual experiments. For presentation our investigation is divided into two sections, one dealing with inhalation experiments and the other with injection experiments. VOM V A LD E T AL.--. INHALATIO Four large-scale inhalation e> laboratory with various forms of gtions, more than 160 animals carried on for periods ranging fi four kinds of asbestos dust emj short fiber, 100 per cent ball-mi K ing's F loa The first inhalation experime; with asbestos dust w as begun ii T able 2.-- Chemical Analy. Type oi Asbestos StOs Fe=Oa AlsOs Cr-Oa King's floats........... .. 39.32 8*84 Short fiber............. .. 37.17 9 J0 9 1.40 0.14 Long fiber............. .. 38.10 5.32 0.78 - Not determined. T able 3.--Petrographic Ana! King's floats *: The approxim ate eotnpt. than 10 microns and reported as percentage serpentine tf , m agnetite 12 , carbonates 18, ti 200 microns long were included. Short flber ): The m aterial, betore beta chrysotile and p la t; (nonflbrous) serpentine, chrysotile IT, serpentine 55, m agnetite 10, qu-. nctinolite and tremolite, 11. Long fiber): The m aterial consisted pri Shreds of nonseparated fibers 5 to 15 micro: present. The approxim ate composition, by netlte 5, brucite 2, other minerals, amonp minerals, 3. Only a trace o f q u a rtz was ob- *Thc analysis of the King's floats act University, has been rrported elsewhere (II i eralogy of Asbestos Dims, J . Indust. H yg. .' t For the sh o rt liber asbestos and the .. supplemented with x-ray diffraction examln periods up to 33 months. Some ; exposure lived for an additiona exposure. A preliminary repor months of exposure. A t that tim< 2'/\ years and the conclusions ; asbestos dust were provisional, 'i results of the completed study, wi Composition and Atmospheric Cone. a commercial variety of asbestos kno' fibers, ranging in length from 1 nun. also varied in size. I t was obtained Asbestos Corporation of America, an<< amount of fibrous chrysotile was only t % V O R W A LD E T AL.--ST U D IE S . O f A X B h W l / IN H A LA TIO N . EXPERIM ENTS * Four large-scale inhalation experim ents have been conducted in this laboratory with various forms of asbestos dust. In each of these investi gations, more than 160 animals were used, and the experim ents w ere carried on for periods ranging from tw o to m ore than five years. The four kinds of asbestos dust employed are designated as K ing's floats, short fiber, 100 per cent ball-milled, and long fiber asbestos dust. K ing's F loats A sbestos D ust T he first inhalation experim ent conducted at the Saranac Laboratory w ith asbestos dust w as begun in 1928. A nim als inhaled the dust for T able 2.-- Chemical A nalysis o f A sbestos D usting M aterials Type of Asbestos Igni tion SIOs FesOa AlsOs CrsOs MnO CaO MgO NasO K ;0 CO* Loss T otal V J King's B oats........... .. 39.32 8.84 * 0.67 35.56 12.74 97.13 Short fiber.............. .. 37.17 9.09 1.40 0.14 0.09 0.85 35.96 0.14 0.20 0.98 14.09 100.11 Long fiber.............. .. 38.40 5.32 0.78 * 0.03 0.31 40.18 0.06 0.06 0.57 14.00 99.76 Not determined. T able 3.-- Petrographic Analysis of A sbestos D usting M aterials King's Boats *: The approxim ate composition, based on particles (except chrysotlle) smaller th a n 10 microns and reported as percentages obtained from particle counts, was chrysotlle 14, serpentine 40, m agnetite 12, carbonates 18, talc 12, other m inerals 4. F or chrysotlle, fibers up to 200 microns long were Included. S hort fiber t: The m aterial, before being ball milled, contained a preponderance o f fibrous chrysotlle and platy (nonfibrous) serpentine. The approxim ate composition, by percentage, was chrysotlle 17, serpentine 55, m agnetite 10, quartz 2, brucite 5, other minerals, including dolom ite, actinolite and tremollte, ll. Long fiberf: The m aterial consisted principally of the fibrous asbestos mineral chrysotlle. Shreds .of nonseparated fibers 5 to 15 microns in diam eter and up to 50 microns In length were, present. The approxim ate composition, by percentage, was chrysotlle 75, serpentine 15, mag* netlte 5, brucite 2, other minerals, among which were calclte and ehloritlc and micaceous minerals, 3. Only a trace of quartz was observed. T h e analysis of the King's floats asbestos, m ade by Dr. O. 8. Ilurlbut J r., of H arvard University, lias been reported elsewhere (U urlbut, C. 8., J r ., and Williams, C. R.: The Mlu* eralogy o f Asbestos Dust, J . Indust. Hyg. & Toxicol. 17: 292, 1935). t For the sho rt fiber asbestos and the long fiber asbestos the petrographic analysis was supplemented with x-ray diffraction examination. periods up to 33 months. Som e guinea pigs with six and nine months' exposure lived for an additional three years after cessation of their ex p o su re. A prelim inary r e p o r tla presented observations after 2 9 m onths of exposure. A t that time observations covered a period of only 2% years and the conclusions as to the ultim ate effects of inhaled asliestos dust were provisional. Those conclusions are substantiated by results of the completed study, which is reported as follows. Composition and Atmospheric Concentration of the Dust.--The dusting material, a com mercial variety of asbestos known as K ing's floats, was composed of sh o rt fibers, ranging in length from 1 mm. to 1 micron or less, and of particles which also varied in size. It was obtained from the Thetford, Quebec, plant of the Asbestos Corporation of America, and analyses (tables 2 and 3) reveal that the am ount of fibrous chrysotile was only 14 per cent, a rath er low value.- 8 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE Impinger samples taken soon after the experiment was started indicated that the dust concentration was at first quite low, the average dust count being only 6.0 million particles per cubic foot of air by the standard light field technic and 0.8 million for particles and fibers greater than 10 microns. After the inhalation experiment had been under way for about two years, the speed of the rotating paddle in the dusting machine was increased and for the remaining 10 months of the experi ment considerably more dust was dispersed into the atmosphere. The average dust count of impinger samples collected after this change was 53.7 million by the usual light field method and 1.6 million for particles and fibers larger than 10 microns. It is probable, however, that the true values of the dust concentration were higher than the counts given in this paragraph. The impinger samples for the King's floats experiment were collected in water, but later studies7 have shovim that counts of impinger samples of asbestos dust taken in water are not reliable. Ethyl alcohol instead of water was used as the collecting fluid in all subsequent experi ments. Table 4.--Summary of Inhalation Experiment with King's Floats Asbestos Dust Nature of Experiment Dust exposure continuous through- out life Dust exposure followed by pro- longed residence in normal air Tuberculous infection * a t sta rt of dust exposure Controls to Infection: no dust cximsurc Tuberculous Infection * after 2Bmo. of dust exposure, then residence in normal air Controls to Infection: no dust exposare Animals 54 guinea pigs Urabbits 18 rats 23 guinea pigs 25 guinea pigs l rabbit 1 rabbit to guinea pigs 22 guinea pigs 12 guinea pigs 12 guinea pigs Maximum Maxi- Survival mum After Dust Ex- Dust Ex posure, posure, Mo. Mo. 33 0 19 0 6 0 6 35 37 6 30 f 19 34 j 35 0 0 35 f * Rsulta Typical peribronchiolar fibrosis a fte r 16 months Foreign body bronchitis Little or no reaction Nonprogressive fibrosis Nonprogressive fibrosis Absorption of foreign body reaction Temporary progression of Infection, followed by healing with fibrosis .Healing by resolution (one exception) 26 14 No appreciable Increase In susceptibility to tuberculous infection; healing with fibrosis 0 i# t Healing by resolution The guinea pigs were infected with tow virulence Ri strain of tubercle bacillus, t This means the survival period following infection. Results of the investigation, briefly summarized in table 4, show that inhalation of King's floats asbestos dust produced a typical peribronchiolar fibrosis in guinea pigs but not in rabbits or rats. Reaction in Normal Guinea Pigs.--Guinea pigs inhaling this dust for periods up to 33 months hadja characteristic fibrosis occurring in conical patches about the respiratory bronchioles. During this exposure the peripheral alveoli were not involved. The particulate elements of the dust were transported through the lymphatic system to the bronchial nodes, causing no significant reaction in either site; the fibrous elements remained fixed at the points of original localization and were seldom detected in the lymph nodes. After exposure of approximately a year a small amount of cellular reaction had been produced about many respiratory bronchioles (fig. 3 A ) . As more dust was inhaled, it continued to accumulate in the same location, and later stages of the disease (fig. 3 B ) consisted of extensions of the original lesions. Apparently, the inhaled fibers were caught in the pocket-like alveoli that are given off from the lateral walls of the respiratory bronchioles. There they 7. Fulton, W . B.; Houtz, R. L .; Dooley, A., and Mathews, J. L .: Asbestosis: I. The Collection and Counting of Asbestos Dust Encountered in Asbestos Fabri cating Plants, Special Bulletin 37, Pennsylvania Department of Labor and Industry, Harrisburg, 1934. VORWAL were phagocytosed, ai cells. Mononuclear lei ing of the bronchiolar v The process evolved fibers steadily increase- Fig. 3.--King's floats i months' exposure. It inch becoming an alveolar duel wall of the bronchiole am. with 28 months' exposure peribronchial fibrosis extern epithelium lining these al (X 200). d isto rte d the rdveol --* VORWALD' ET AL.--STUDIES OF ASBESTpSIS 9 were phagocytosed, and many of them were carried into the wall by migratory cells. Mononuclear leukocytes attracted to the area caused an appreciable thicken ing of the bronchiolar wall. After 16 months a delicate fibrosis made its appearance. The process evolved gradually, and the number of fine intercellular collagenous fibers steadily increased. As this fibrous deposit contracted, it partially closed and Fig. 3.--King's floats inhalation experiment: A , lung of a guinea pig with 12 months' exposure. It includes a respiratory bronchiole, at the left, branching and becoming an alveolar duct, at the right. Note the accumulation of cells in' the wall of the bronchiole and in adjacent-alveoli (X 130). B , lung of a guinea pig with 28 months' exposure. The field includes a bronchiole, at the center, vvith peribronchial fibrosis extending into the walls of adjacent alveoli. Note the cuboidai epithelium lining these alveoli. This is the so-called "adenomatoid" appearance (X 200). distorted the alveoli -'-''t chronic pulmonary inflammation resulting from many causes. Willis * described a similar structure in the lungs of guinea pigs inhaling silicon carbide. The longer asbestos exposures resulted only in more thickening of the walls of the air spaces, largely due to an increase in the amount of fibrosis. The fibrous tissue always remained cellular and failed to show the hyalinization characteristic of silicosis. Fig. 4.--King's floats inhalation experiment: A , lung of a guinea pig with six months' dust exposure followed by 35 months' inhalation of normal air. The reaction is rather slight, but distinct fibrosis is present ( X 200). Note tliat 28 months of continuous exposure (fig. 3 B ) produces much more extensive reaction. B, lung of a guinea pig exposed to the asbestos dust for nine months and liv in g th e re a fte r in n o rm al a ir fo r 37 months. The reaction shown is more than that in A but much less than the reaction in figure 3 B ( x 200). 8. Willis, H . S., and Brutsaert, P .: Tumor-like Structures in the Lungs of Guinea Pigs Artificially Exposed to Silica Dust, Am. Rev. Tuhcrc. 17:268, lO-'.o V01<WALD ET -At.--STUDIES OE ASBESTOSIS 11 Asbestosis bodies (fig. 2 B ), first seen in the lungs of the guinea pigs that had inhaled,dust for,about two months, became more numerous and more distinctly segmented with increasing exposure. The reaction produced in guinea pigs exposed for six and nine months did not progress significantly during a subsequent period of 35 and 37 months when the animals lived in a normal atmosphere (fig. 4). Between eight and 11 months after exposure ceased, the cellular reaction in the lung had been completely replaced by thin strands of fibrous tissue. At later periods the scar tissue was less in amount, but in the last animal killed, 37 months after discontinuing dust exposure, some fibrosis was still visible. Reaction in Guinea Pigs Infected with Tubercle Bacilli at the Onset of Dust Inhalation.--Of the group of 40 guinea pigs infected with attenuated tubercle bacilli, Ri strain,8 at the time that dust exposure was begun, 31 died or were killed before the completion of two years of the exposure and were reported in the paper by Gardner and Cummings.18 Seventeen of these died from intercurrent pneumonia. Briefly, the results were as follows: Ten revealed some evidence of spread of the tuberculous process (fig. 5 A ) ; in 6 of these it was confined to the lungs, and in the other 4 the abdominal viscera also were involved. Extension of the infection was first seen after seven months of dust inhalation; during the next 20 months more than half of the animals showed actively spreading tuber culosis, and in 3 of them small cavities had developed. During the last eight months no animals exhibited any evidence of active infection although in half of them the healed fibrous scars of previous spreads were obvious. The scars were more extensive than is characteristic of either tuberculosis or asbestosis alone. The nine animals which were still alive after two years of dust exposure were killed at intervals during the following year. In four of them the primary foci of infection were healed with fibrosis and even calcification, and there was no evidence of progression (fig. S B ) . In the remaining five the tuberculous foci showed evidence of having previously spread locally; in four of them, by the time of autopsy, the foci were healed, with excessive fibrosis; in the fifth animal there was a generalized chronic tuberculous pneumonia in one lobe, and in the other lobes there were isolated primary tubercles, which were still active but had not spread. Reaction in Guinea Pigs Infected with Tubercle Bacilli After Establishment of Asbestosis.--Twelve guinea pigs, after inhaling King's floats asbestos dust for 26 mouths, were infected with tubcrrlc bacilli and then removed to normal air. Six of these animals died within seven weeks, five from intercurrent nontuberculous infection. The remaining six animals were killed at intervals up to 14 months after infection. The subpleural tubercles were no more numerous in the dusted animals than in the nondusted controls, but a considerable number were found in the depths of the lung about foci of asbestosis. The tuberculous component of the combined reaction showed only slight local extension about lesions in the lungs and tracheobronchial lymph nodes. Caseation was found in tubercles \ l/ t months old, but by S'A months it had completely disappeared, leaving only scar tissue. Foci of fibrosis still persisted in the last animal, which was killed 14 months after infection. Reaction in Rabbits.--Rabbits exposed to the asbestos dust for periods up to 19 months showed a foreign body type of reaction of low grade, but no fibrosis. Although their lungs contained particulate elements of the dust, fibers were not present, indicating that the upper respiratory mechanism of the rabbit is adequate to exclude fibrous foreign bodies. Two rabbits, after inhaling dust for six and 199 9. Steenken, W., Jr., and Gardner, L. U .: Ri Strain of Tubercle Bacillus: Its Dissociation and Virulence of Variants in Normal and Silicotic Guinea Pigs, Am. Rev. Tul>erc. 54:51, 1946. 12 IN D U S T R IA L H Y G IE N E A N D O C C U P A T IO N A L M E D IC IN E months, lived in normal air for more than two years. A t autopsy neither animal showed any evidence of cellular reaction or fibrosis in the terminal bronchioles, nor were there any asbestosis bodies. Reaction in W hite R ats.--All the rats had acquired an infection, resulting in the formation of pulmonary abscesses, before they came to autopsy. Apparently, so much heavy mucus obstructed their bronchi that very few fibers could have entered _ Fig. 5.--King's float inhalation experiment: A , lung of guinea pig infected with Ri tubercle bacilli and then exposed to dust for 24 months. A bronchiole is shown just above center. Surrounding it is some collagen deposition, together with typical epithelioid cell infiltration of the wall. Note the lack of encapsulation and the peripheral epithelioid cell pneumonia, which illustrate a spreading tuber culous process (X 2 0 0 ). B, lung of a guinea pig infected with Ri tubercle bacilli and then exposed to dust for 35 months. _Note the subplcural distinctly encapsulated caseous focus, the calcification at the right border of the lesion and the absence of cells in adjacent alveoli, all of which illustrate a healing tuberculous process (x 2 0 0 ) . VORWALD ET A t, their lungs. In a few of the rats, but there was no fibrosis. T his pi cessful. Sum m ary and Interpretatio F loats D u st.-- T he findings in t be sum m arized under tw o hea< 1. Effect of the inhaled floats dust caused a charactei pigs but not in rabbits or rats, in extent after the dust exposur 2. Effect of the inhaled dust pigs infected with attenuated dust room, the results were m ment of this type. A few anin infection; in most of them ther w ith subsequent healing; in on< active to death. In contrast, v exposed to quartz dust instear continues to progress and eve: O n the other hand, infected ani oxide do not show any proginfected with attenuated tuber years' asbestos dust exposure only modification o f the infect: being retained in the peribn forming there in addition to In view of the variability < response and the high proport monia, it is felt that only tern asbestos dust on the course of experim ent. S hort F r Since hazardous dusts like fibrosis when the particles are experim ent was performed to for asbestos dust. It was th consisting almost entirely of fil would initiate an accelerated t reaction in a shorter time thai tained fibers from 1 mm. to 1 r particulate matter. Composition and Atmospheric C. for this experiment was the remain fabricating plant after a carding o]10 10. Vorwald. A. J . ; P ratt, P . C .. D. A .: Siderosis: A Benign Pneutni Indust. Afed. * Surg. 19:170. 1<)?0. VORWALD ET At..--STUDIES OF ASBESTOSIS 13 their lungs. In a few of the rats, an occasional asbestosis body was discovered, but there was no fibrosis. This phase of the experiment was considered unsuc cessful. Summary and Interpretation of Inhalation Experiment with King's Floats Dust.--The findings in the experiment with King's floats dust can be summarized under two headings: 1. Effect of the inhaled dust on normal animals. The King's floats dust caused a characteristic peribronchiolar fibrosis in guinea pigs but not in rabbits or rats. The fibrosis did not increase significantly in extent after the dust exposure was discontinued. 2. Effect of the inhaled dust on tuberculosis in guinea pigs. In guinea pigs infected with attenuated tubercle bacilli and then placed in the dust room, the results were more variable than is usual in an experi ment of this type. A few animals showed no sign of progression of the infection; in most of them there was evidence of temporary progression with subsequent healing; in one animal the tuberculous process remained active to death. In contrast, when guinea pigs after being infected are exposed to quartz dust instead of asbestos dust, the infectious process continues to progress and eventually causes the death of the animals. On the other hand, infected animals exposed to a harmless dust like iron oxide do not show any progression of the infection.10 Guinea pigs infected with attenuated tubercle bacilli after the termination of two years' asbestos dust exposure did not show progressive disease. The only modification of the infection was in its localization, a few bacilli being retained in the peribronchiolar fibrous tissue, with tubercles forming there in addition to the usual tubercles beneath the pleura. In view of the variability of the results, the unusual nature of the response and the high proportion of deaths due to intercurrent pneu monia, it is felt that only tentative conclusions as to the influence of asbestos dust on the course of tuberculous infection aire justified by this experiment. S hort F iber A sbestos D ust Since hazardous dusts like quartz are most effective in producing fibrosis when the particles are 3 microns and less in size, an inhalation experiment was performed to determine whether this condition is true for asbestos dust. It was thought that a short fiber asbestos dust consisting almost entirely of fibers and particles smaller than 3 microns would initiate an accelerated tissue response and produce an advanced reaction in a shorter time than did the King's floats dust, which con tained fibers from 1 mm. to 1 micron and less in length as well as much particulate matter. Composition and Atmospheric Concentration of the Dust.--The dusting material for this experiment was the remains of fibers collected in dust bins of an asbestos- fabricating plant after a carding operation and screened to pass 200 mesh. Since10 10. Vorwald. A. J . ; Pratt, P. C .; Durkan, T. M .; Delahant, A. B,, and Bailey, D. A.: Siderosis: A Benign Pneumoconjosis Due to the Inhalation of Iron Dust, Indust. Med. & Surg. 19:170. 1950. 14 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE the material as received contained many long libers, it was ground in a steel ball mill to reduce practically all the particles to 3 microns or less in size. When used alone in the standard dusting machine, this finely ground asbestos tended to pack in the hopper, and it became necessary to mix one volume of the unground material with three volumes of the ground to generate a satisfactory dust cloud. It is pertinent to mention here that the addition of the small quantity of unground asbestos was unfortunate, because it confused the interpretation of results. The composition of the short fiber asbestos as received is disclosed by the chemical and petrographic analyses given in tables 2 and 3. Samples taken before and after grinding yielded about the same values on analysis, indicating that there was no contamination from the mill or loss of water content. The dust concentration varied during the experiment, the light field counts for atmospheric samples collected inside the animal cages with the impinger apparatus ranging from 83 million to 182 million. The average of counts was 130 million for the first year of the experiment, 134 million for the second year and 140 million for the third year. Size-frequency measurements of air-floated dust from inside the cages at a magnification of 1,300 X revealed a great preponderance of fine particles, nearly*10 Table 5.--Summary of Inhalation Experiment witk Short Fiber Asbestos Dust Mature ot Experiment Dust exposure continuous through out life Animals 46 guinea pigs 73 rats 18 cats 7 rabbits Dust exposure followed by prolonged residence In normal air 13 guinea pigs Scats 1 rabbit Maximum Maxi- Survival mum After Dust Ex- Dust Ex posure, posure. Mo. Mo. 34 0 32 0 54* 0 47* 0 20 14 31 24 62* Results Rate of reaction about the same as in experi ment with King's floats asbestos but extent of involvement very much less t Characteristic patches of peribronchiolar fibro sis; no asbestosis bodies Subpleural reaction only No fibrosis seen grossly; microscopic evidence of alveolar wall thickeniug after 46 months' exposure Progression after removal from dust doubt ful--neither clearly established nor definitely excluded Same as for continuous exposure Similar to continuous exposure; evidence of slight regression * After 33 months the animals were exposed to 100 per cent hall-milled asbestos. t The reaction was probably due to long fibers in the unground material which was mixed with the ground asbestos dust to produce a satisfactory dust cloud. 90 per cent of the particles seen being smaller than 3 microns. It was estimated that approximately 1 per cent of the dust was in the form of fibers greater than 10 microns in length. ! Four species of animals--guinea pigs, white rats, cats and rabbits--were used in this experiment. The results of the dust exposure, summarized in table 5, are presented in greater detail below. ' Reaction in Guinea Pigs.--Eighty guinea pigs were originally placed in the dust room, hut 21 of them were later eliminated from the experiment and killed because of enlargement of the cervical lymph nodes thought to be due to intercurrent infection of the upper respiratory tract. Of the other 59 animals, 46 remained in the dust room until they were killed or died at periods up to 34 months, and 13 | animals were transferred to normal air after being exposed to the dust for 20 j months. , The type of tissue reaction provoked by the inhaled short fiber asbestos was essentially the same as that already observed in the experiment with King's floats asbestos. The rate of reaction also was approximately the same, but the extent of involvement was very much less. After 16 to 24 months of exposure only a very r . . n f .r . < " . VORWALD Ei Only after exposures ha< appreciable tendency for du 16 months phagocytes had < bronchioles which revealed cells. There were also son foreign body type. A t 20 ti prominent, and sometimes cl o r "adenomatoid'' appearance ing the experiment with the ! of the series the reaction development of fibrous tiss iagen was pale in color an< Diffuse chronic pleurisy wa T able 6.-- Analyses o f Lus Exposure to Dust, Mo. 12 Period A in Normal Air, Mo. I> Dust 0 15 0 20 0 24 0 30 ; 34 Dust Exposure Fo) 20 ! 20 10 ' ( 20 M 1 * The symbols averaging the ti the relative degree o t reaction, raexperiment). The relationships a symbols In other tables. monary infection. This sugg asbestosis, but the evidence is of the tracheobronchial lympli experiment with King's floats been transported to the nodes reaction was essentially an in< original cells being preserved i In the group removed to no: sion of disease was not definit disproved, owing to the vari. reactions, from mild to sever the length of time after cessa to- variation in individual sus chemical analyses (table 6 ), wh in lungs with widely different VORWALU ET AL.--STUDIES OV ASBESTOSIS 15 Only after exposures had continued for approximately one year was there an appreciable tendency for dust-containing phagocytes to gather into clumps. By 16 months phagocytes had collected about the walls of a few of the respiratory bronchioles which revealed a little proliferation or infiltration of mononuclear cells. There were also some multinucleated cells, but they were of the inert, foreign body type. At 20 to 24 months the cellular clumps were sometimes quite prominent, and sometimes changes in the epithelium resulted in the adenoma-like or "adenomatoid'' appearance (fig. 3 B ) previously described in the section review ing the experiment with the King's floats dust. In most of the subsequent members of the series the reaction remained cellular, but a few exhibited pronounced development of fibrous tissue. In these few members of the series the col lagen was pale in color and tenuous, with no appearance of being hyalinized. Diffuse chronic pleurisy was present in a few animals without evidence of pul- T able 6.-- Analyses of Lungs of Guinea Pigs After Prolonged Inhalation of Short Fiber Asbestos Dust Exposure to Dust, Mo. 12 IS 20 24 30 34 20 20 20 Period In Normal Air, Mo. Amount of Ash, % of Dried Lung Total 810s, % of Dried Lung Total SIO-, % ot Ash Dust Exposure Continuous During Life 5.02 0.61 10.23 0 4.53 0.46 10.08 5.16 0414 10.54 5.00 0.49 9.96 0 4.76 0.43 9.00 4.05 0.53 10.60 0 5.86 6.43 0.85 0.90 14.46 14.07 0 5.42 5.50 0.78 0.78 14.48 ' 14.20 0 5.35 ; 6.55 0.96 1.27 17.89 19.46 AV 6.06 6.35 0.75 0.96 12.37 15.11 Dust Exposure Followed by Prolonged Residence In Normal Air 4 1 5.16 ! 5.11 0.48 0.36 9.30 7.16 10 1 6.11 t 3.98 0.62 0.34 10.21 8.51 4.77 0.25 5.31 14 ! 6.18 0.26 5.00 4.77 0.22 4.60 Tissue Reactlo 2+ 3+ 4+ 4+ 2+ 8+ 2+ * The symbols averaging the tissue reaction In each group ot guinea pigs represent merely the relative degree of reaction, ranging from (questionable) to 4+ (the maximum for this experiment). The relationships apply only within this table and cannot be compared with symbols In other tables. monary infection. This suggests that pleurisy may be a specific concomitant of asbestosis, but the evidence is not adequate to establish this point. The reaction of the tracheobronchial lymph nodes was more pronounced than in the previous experiment with King's floats asbestos, probably because more fine particles had been transported to the nodes in animals inhaling short fiber asbestos. The nodal reaction was essentially an increase in reticulum, rather than a fibrosis, with the original cells being preserved between the thickened reticular fibers. In the group removed to normal air after 20 months' inhalation of dust, progres sion of disease was not definitely demonstrated, but neither could it be absolutely disproved, owing to the variability of the response in different animals. The reactions, from mild to severe, occurred sporadically and bore no relationship to the length of time after cessation of exposure. The differences were attributed to' variation in individual susceptibility. This view received support from the chemical analyses (table 6), which revealed comparable amounts of ash and silica in lungs with widely different amounts of tissue change. For example, the ash 16 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE and silica values were quite similar for three animals living in dust 20 months and then in normal air for 14 months, yet the tissue reaction was severe in one animal, mild in another and only doubtful in the third. The formation of asbestosis bodies was at first extremely limited in both groups. After five months' exposure only a very rare short body could be found, usually inside a cell. Some of the finest intracellular particles were surrounded by yellow deposits having the same color as the asbestosis body. One year's exposure had per mitted an accumulation of many longer fibers, a number of which were coated and seen as typical asbestosis bodies. Most of these were still short enough to be partially or entirely within phagocytic cells. By the twentieth month and thereafter they T able 7.--Analyses of Lungs of While Rats That Had Inhaled . Short Fiber Asbestos Dust Duration of Exposure, Mo. 0* 4 Amt. ot Ash, % ot Dried Lung 43..39 2.9 3.6 3.3 3.9 3.4 '33..56 2.9 U .2 3.3 L 33..4 Total SIOs, % of Dried Lung 0.00 0.00 0.00 0.00 0.00 0.00 0.00 o.os 0.13 0.0 0.05 0.08 0.11 oxn Total 8102, % Of Ash 0.0 : * 0.0 > 0.0 0.0 0.0 0.0 0.0 23..13 3.2 1.5 2.3 3.0 2.2 Duration of Exposure. Mo. 6 81 10 Amt. of Ash,% of Dried Lung Total StO, % of Dried Lung f 8.3 0.07 { 3.4 0.03 [ 3.7 )' 0.04 f 3.9 0.08 8.6 0.18 { 3.5 0.15 4.4 0.17 1 3.7 0.16 (4.0 0.18 I 4.8 0.15 1 5.3 0.15 1.4.7 0.13 Total 8IO2, % of Ash 2.1 1.5 i.i 2.2 5.5 3.4 4.0 4.2 3.8 3.3 2.8 2.8 * Normal controls (no dust exposure). T able 8.--Average Values of Ash and Total Silica for Lungs of White Rats Inhaling Various Dttsts for Various Periods (Lungs Only, Without Included Lymph Nodes) Dura tion of Exposine, Mo. 2 4 6 8 10 Amt. ot Ash, % ot Dried Lung Short Fiber Asbes tos 3.3 3.4 3.5 3.8 4.9 Quartz 4.3 4.5 7.1 4.6 7.8 GypsumFerra- Quartz ginous Mix Chert ture 5. :, 2. 8. 3.8 9. 3.4 9.0 3.6 14-1 , 4.1 Total Short Fiber Asbes tos 0.09 0.09 0.05 0.15 0.15 SiOi, % of Dried Lung Quartz 051 0.51 2.94 1.44 4.40 GypsumFerruJ , Quartz ginous ' Mix Chert ture . 0.25 0.06 0.32 0.07 3.45 0.11 2.40 0.32 6.09 0.23 Total SIOs, % of Ash Short Fiber Asbes tos 2.6 2.5 1.6 3.9 3.2 Quartz 11.7 11.4 41.5 29.4 56.6 GypsumFerru- Quartz ginous Mix Chert ture 3.9 2.6 3.6 2.0 34.4 3.4 26.5 9.1 43.2 6.7 were relatively numerous although still rare in comparison with the findings in the King's floats experiment. Reaction in White Rats.--Seventy-three white rats were exposed to atmospheric short fiber asbestos dust lor periods up to 32 months. During the first 10 months animals were killed bimonthly and for the remainder of the experiment at less frequent intervals. Up to eight months the dust cells were widely scattered and existed in foci only sporadically. Reaction was limited to occasional slight thicken ing of the- septums about small accumulations <ff dust cells. At 10 months there was a suggestion of early fibrosis in a few rats, but the change was so slight that it would probably have been overlooked without the clump of dust cells which attracted attention to the area. Only 10 animals were exposed for from 12 to 32 months. In each of them the lungs contained minute foci of well defined fibrosis distributed like that of asbestosis but without asbestosis bodies. The lesions, visible only at a magnification of 150 diameters or more, consisted of natehe alone VORWALD ET kL .--STUDIES OF ASBESTOS1S 17 alveolar ducts in which the walls of the associated air spaces were very thick, owing to swollen collagen framework. Connective tissue and Foot-Bielschowsky silver preparations revealed complete loss of capillary bed locally. Outside the collagen was a thin layer of epithelial cells. This did not resemble the "adenomatoid" change characteristic of guinea pig asbestosis. Near the lesions the air spaces were filled with phagocytes containing gray to yellow particulate dust and a rare, long, naked asbestos fiber. Careful,- search failed to reveal even a suggestion of an asbestosis body. Pleurisy was absent. The tracheobronchial nodes showed com pact focal collections of monocytic cells at 12 months and, at 20 months, some diffuse thickening of the reticulum. In a few rats there was definite fibrosis along the margins of the node, extending into the mediastinal areolar tissue. Results of chemical analyses made on the white rats are given in table 7, and the average values have been recorded in table 8 for comparison with similar values for rats inhaling other dusts. It will be noted that the values for asbestos are lower than those for quartz or chert but approximate those for the gypsumquartz mixture, in which atmospheric agglutination tended to reduce the amount of dust inhaled. This condition prevailed even though the atmospheric concentra tion of asbestos dust was essentially the same as that of the quartz, was one-half that of the gypsum-quartz mixture and was one-fifth that of the ferruginous chert. Since the values for asbestos are low, it might be inferred that the total quantity of that dust actually inhaled was small or that it had been eliminated from or dissolved within the lungs. Evaluation of these possibilities is not feasible on the basis of the observations derived from this study. Reaction in Cats.--Twenty cats were used in this inhalation experiment with the short fiber asbestos. Eighteen were kept in the dust room continuously until put to death, the exposure period ranging from one month to nearly 54 months. The other two were removed to normal air after a dust exposure of 31 months; one of these was killed five months, and the other 24 months, later. In general, the tissue response was confined to microscopic foci of fibrosis, which were in the walls of groups of subpleural alveoli rather than in the peribronchiolar areas. In one animal the change was extensive enough to be visualized on gross inspection of the section. Only in the animal with the longest exposure--54 months--did the roentgenogram reveal definitely abnormal shadows. A roentgenogram made after 30 months revealed no abnormality; after 45 months, a faint mottling could be detected throughout both lungs. At autopsy, nine months later, there was only microscopic fibrosis in the subpleural zone plus heavy lymphocytic infiltration about small bronchioles. Asbestosis bodies were rare. On prolonged search a few yellow atypical bodies, smooth and without haustrations, were found in two animals exposed for more than a year. Reaction in Rabbits.--Eight rabbits were exposed to dust for'periods extending from one to more than five years; the last animal was removed from the dust room and left in normal air six months before being killed. There was never enough pulmonary fibrosis to be detected grossly, and there was no chronic adhesive pleurisy. Microscopic evidence of alveolar wall thickening was .first detected in one animal after about three years of exposure and was seen in all five animals examined thereafter, including the one removed to normal air. One animal that died of paralysis after nearly four years of exposure exhibited a reaction visible on gross inspection of tissue sections. The possibility of pulmonary infection in this animal could not be excluded. In another animal dying two years later the focal fibrosis was not nearly as obvious or as advanced. Areas of involvement, which were largely visualized because of phagocytic reaction within the air spaces,tended microscopically to become more fibrous with the passage of time, but there was never much encroachment on the lumen of air spaces and the structure of the lung was preserved. Asbestosis bodies were not detected in rabbits that died early in the experiment but were seen in all animals that had been exposed to the dust for more than throe rears. 18 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE Sum m ary and Interpretation of Inhalation Experiment with Short Fiber Asbestos Dust.--The original purpose of the experiment was to evaluate the role of short asbestos fibers in the genesis of asbestosis. It was felt also that if the tissues reacted more rapidly and more extensively to short fiber asbestos than to King's floats there would be a basis for believing that the action of asbestos is in part, at least, a chemical one as postulated for quartz. This experiment, in which the tissue reaction was slower and less extensive than that in the previous experiment with King's floats dust, indicates that the capacity of inhaled asbestos fibers to produce fibrosis is determined primarily by factors not chemical in nature. Of the four species exposed in this experiment, only the guinea pig and to a lesser extent the white rat responded with characteristic peri bronchiolar fibrosis. The cat reacted with atypical subpleural fibrosis and the rabbit with only slight parenchymal fibrosis. Ball-M illed A sbestos D ust In the inhalation experiment with short fiber asbestos dust a small quantity of unground short fiber asbestos was mixed with the ballmilled product in order to generate a suitable dust cloud. When that experiment failed to produce an accelerated tissue reaction, in com parison with the response initiated by King's floats, it became apparent that the biologic activity of asbestos is not increased by a reduction of fiber size. Thus the possibility arose that the tissue reaction observed was due solely to the relatively few long fibers of the unground asbestos and that the short fibers of asbestos had no more than a very insignificant role in the production of asbestosis, a concept not in accord with previous experiments concerning pneumonoconiosis. Consequently another inhalation experiment was started in which only ball-milted asbestos was used. Composition and Atmospheric Concentration of the Dust.--The dusting material was the ball-milled, short liber asbestos used in the previous inhalation experiment, but unground material was not mixed with it. Owing to the tendency of the material to form small spherules which prevented much of the fibrous portion from floating out of the dusting machine, the dispersal of the dust was not entirely satisfactory. Therefore, after an initial seven months of operation, steel wire brushes were attached to the inside surface of the hopper and to the rotating paddle to disintegrate the spherules and release the fibers. This arrangement gave satis factory results and was used for the remaining 21 months of the experiment. The composition of the raw asbestos used is shown in tables 2 and 3. Petro graphic and x-ray diffraction examination of atmospheric dust, collected in the dust room with an electrostatic precipitator after the installation of wire brushes, indicated that about 15 per cent of the air-suspended material was chrysotile, and about 60 per cent, serpentine; of the balance, magnetite comprised 10 per cent, brucite 3 per cent, quartz 2 per cent and other minerals 10 per cent During the seven month period before the wire brushes were used, the chrysotile content of the atmospheric dust was somewhat lower than 15 per cent, but reliable values were not obtained. The dust concentration during the first seven months of the experiment was VORWALD ET AL.--STUDIES OF ASBESTOSIS 19 installed, the dust counts were higher, and the over-all average for the remaining 21 months was about 150 million. Size-frequency studies of atmospheric dust collected inside the animdl cages revealed that nearly 99 per cent of the components suspended in the air could be classified as clumps or particles; only about 1 to 1.5 per cent was fibers. One third to one half of the fibers were longer than 10 microns, indicating a concentration of long fibers of about 0.8 million. This figure is about one-half the estimated value of 1.4 million for the short fiber experiment. Guinea pigs, rats and mice were used in the inhalation experiment with the 100 per cent ball-milled asbestos dust. The results are summarized in table 9. Reaction in Guinea Pigs.--The experiment was started with 100 guinea pigs. As the dust exposure proceeded, there were 39 accidental deaths, 32 of these being due to pneumonia in an epidemic. The 61 pigs remaining exposed to the dust were killed at intervals during exposure, except for 16 guinea pigs transferred to normal air after 28 months of dusting. For the first year of exposure practically the only reaction to the dust was the presence of scattered phagocytes and an occasional minute asbestosis body. At 16 and 20 months no gross response was visible on the tissue section, but microscopically peribronchiolar foci of inflammatory cells T able 9.--Summary o] Inhalation Experiment with 100 Per Cent Ball-Milled Asbestos Dust Nature of Experiment Dust exposure con* tiouous through. out lite Dust exposure fol lowed by pro longed residence In normal air Animals 84 guinea pigs 40 r a ts 24 mice 10 guinea pigs Maxi mum Dust Expo sure, Mo. 24 20 12 28 Maximum Survival After Dust Expo sure, Mo. 0 0 0 12 Results No appreciable pulmonary reaction No suggestion of asbestosis No suggestion of asbestosis Fibrosis typical of asbestosis was present 12 mo. after exposure ceased in an amount sufficient to be visible grossly; smaller tod could be seen microscopically at 2 mo. and 8 mo. after termina tion of exposure could be seen. At 24 months (fig. 6 A ) there was still no change large enough to be seen with a hand lens, although microscopic examination revealed cellular accumulations about terminal bronchioles and many more asbestosis bodies, chiefly within cells. The lungs of animals exposed for the full dusting period of 28 months and afterward living in normal air for two months revealed the changes described above and also very slight peribronchiolar fibrosis. For exposed animals living eight months in normal air the findings were similar, but at 12 months three of four animals showed grossly visible characteristic peribronchiolar fibrosis with adenomatoid change (fig. 6 B ). The tracheobronchial nodes were essentially normal until exposure had been continued for more than a year and a half. Animals killed at 12 months and at 16 months revealed a few minute collections of phagocytes containing particles but practically no fibers large enough to be recognized as such. After 20 months of exposure many monocytes filled with yellow granules were present. At 30 months there had been a slight increase in reticulum but no fibrosis. No further changes occurred in the nodes. Asbestosis bodies were not seen in the nodes of any of the guinea pigs. Minute asbestosis bodies were observed in the lungs as early as three months after exposure began, but they did not become numerous until 16 months had elapsed. The bodies were short and practically all were intracellular, althoneh at important to note that in the later months of exposure there was a distinct increase in the number of long fibers, up to 70 microns in length, in the lungs with the formation of characteristic long asbestosis bodies. Chemical analyses (table 10) of the lungs revealed that considerable dust had been retained in the lungs. After 24 months of continuous exposure the average Fig. 6.--Ball-milled asbestos inhalation experiment: A , lung of a guinea pig w ith 24 m onths' dust exposure. A bronchiole is shown at the center, w ith a slight accumulation of phagocytic cells but without the formation of collagen ( x 200). B, lung of a guinea pig with 28 months' dust exposure and then 12 months' inhalation of normal air. The reaction is much like that shown in A , but there is a slight deposition of collagen, most apparent at the left ( x 200). value for total silica, per cent of ash, was 25.37. This should be contrasted with the average value of 14.34 (table 6) for animals exposed 24 months to the short fiber asbestos dust. In view of the high value 100 per cent ball-milled dust, i was much less than that of . asbestos in the previous expcrii of asbestos inhaled into the lun Reaction in W hite Rats a> for periods up to 20 months a: species did even a suggestion phagocytosis of inhaled partic free in air spaces or were tra asbestosis bodies were found small, nonhaustrated forms wi; T able 10.--Analyses of L un< Experiment with 1< Exposure to Dust, Mo. i Period Id Normal A Air, Mo. Di Dust f 0 2 0 1 3 0 6 0 i 8 0 12 o ; 16 i 20 0 ! 24 ; Dust Exposure Fol 28 2 ) 28 8 1 28 12 | * The symbols averaging the degree of reaction, ranging from o experiment). The relationships at symbols in other tables. Summary and Interprc Cent Ball-Milled Asbestos experiment was not as int< short fiber asbestos. The extensive even though m or were fewer fibers longer experiment, the results tei summary of the previous primarily chemical in natir tion in size of asbestos fib., asbestos inhaled into the lut VORWALD ET AU.--STUtlES OF ASBESTOSIS 21 In view of the high values for silica obtained with the animals exposed to 100 per cent ball-milled dust, it is important to note that their pulmonary response was much less than that of animals exposed for 24 months to the short fiber asbestos in the previous experiment. This again indicates that the biologic activity of asbestos inhaled into the lung is not increased by a reduction in size of the fibers. Reaction in White Rats and Mice.--In this experiment 40 rats were exposed for periods up to 20 months and 24 mice for periods up to 12 months. In neither species did even a suggestion of asbestosis develop, and reaction was limited to phagocytosis of inhaled particles by widely scattered dust cells which remained free in air spaces or were transported to the tracheobronchial lymph nodes. No asbestosis bodies were found in the rats, but in the mice there were a very few small, nonhaustrated forms within phagocytes. T able 10.--Analyses of Lungs of Guinea Pigs Exposed to Dust in Inhalation Experiment with 100 per Cent Ball-Milled Asbestos Dust Exposure to Duet, Mo. 1 s 5 8 12 16 20 24 28 28 Period Id Normal Air, Mo. Amt. of Ash, % of Dried Lung Total SIOs, % ot Dried Lung Total SlOt, % of Ash Tissue Reaction * Dust Exposure Continuous During Life 4.85 0.21 4.26 0 4.30 0.30 7.05 4.35 0.24 6.60 0 4.60 0.23 4.90 0 4.60 0.34 7.40 $.05 0.61 12.01 0 5.60 0.70 12.47 0 5.07 0.32 6.38 5.74 0.56 .77 0 5.10 0.38 7.51 0 5.08 0.38 7.17 5.02 0.3 7.72 0 0 4.35 0.52 11.86 0 0 3.65 6.24 1.25 22.16 1.45 23.28 0 0 5.40 5.01 1.02 18.96 1.11 21.95 + 5.65 1.28 22.00 5.20 1.28 24.61 6.30 " t 5.56 1.85 20.06 1.21 21.70 Dust Exposure Followed by Prolonged Residence In Normal Air i 7.25 8.07 1.57 21.63 2.19 25.24 + , i 5.25 0.68 12.99 ! 5.96 0.87 14.55 + 12 \ 6.38 6.17 0.84 13.08 0.61 12.41 2+ * The symbols averaging the tissue reaction In each group represent merely the relative degree of reaction, ranging from O t o (questionable) to 2+ (the maximum observed In this experiment). The relationships apply only within this table and cannot be compared with symbols in other tables. Summary and Interpretation of Inhalation Experiment with 100 per Cent Ball-Milled Asbestos Dust.-- The tissue reaction observed in this experiment was not as intense as that in the previous investigation with short fiber asbestos. The reaction was slower in development and less extensive even though more dust accumulated in the lungs. Since there were fewer fibers longer than 3 microns in the material used in this experiment, the results tend to confirm th e in terp retatio n made in the summary of the previous short fiber experiment that the reaction is not primarily chemical in nature, and to support the impression that reduc tion. in size of asbestos fibers does not increase the biologic activity of asbestos inhaled into the lung. 22 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE The finding of long asbestosis bodies in animals that had inhaled the ball-milled material is an example of the difficulty of completely eliminat ing long fibers from a large volume of asbestos as required for an inhalation experiment. In regard to the progression of the tissue reaction after the animals had been removed from the dust, observed in this experiment but not in the others, the following interpretation is offered: When the reaction is well developed at the termination of exposure, the contraction of the fibrous tissue obscures any progression that may have occurred; in this experiment, however, since the reaction observed was less mature, its subsequent progress was more readily apparent. L ong F iber A sbestos D ust Since inhalation of short fiber and of 100 per cent ball-milled asbestos dust did not result in acceleration of the tissue reaction in comparison with that produced by King's floats, the hypothesis that short fibers of asbestos were of minor importance in the etiology of asbestosis was given added support, and attention was directed, to the view that the long fibers were of primary significance in that etiology. The King's floats asbestos used in the first inhalation experiment had a rather low content of fibrous chrysotile and contained considerable serpentine and other impurities. Therefore, it was decided to conduct a new inhalation experiment with a purer form of chrysotile which would be richer in long fibers. ( m position ami Atm ospheric Concentration of the Dust.--The dusting m aterial employed in this investigation was obtained front an asbestos fabricating plant. Samples of several varieties of long fiber asbestos dust were first submitted to the Saranac Laboratory for examination, and one of these, which was low in magnetite and chromite and had a fibrous content estimated to be about 75 per cent, was selected as most suitable. Steel wire brushes, fastened to the inside surface of the hopper and to the rotating paddle as in the preceding inhalation experiment, were used to open up the bundles of asbestos and liberate more fibers into the atmosphere. The composition of the long fiber asbestos used is indicated by the chemical and petrographic analyses given in tables 2 and 3. Analysis of air-suspended m aterial from the dust room disclosed that about 60 per cent of the long fiber dust was chrysotile and about 20 per cent serpentine; as already noted, the composition of a sim ilar air-floated sample of ball-milled, short fiber dust was 15 per cent chrysotile and 60 per cent serpentine. T he dust concentration as revealed by impinger samples taken inside the animal cages was much lower than the concentration for the experiments with short fiber or ball-milled dust. For the first year of the experiment with long fiber asbestos the average of the light field counts was 32 million particles per cubic foot of a i r ; for the second year, 48 m illion; for the third year, 39 million, and for the fourth year, 43 million. / The size-frequency of atmospheric samples of the long fiber asbestos dust and of the ball-milled dust is shown in table 11. Both samples were collected with the electrostatic precipitator. It will be noted that there was far more fibrous material in the long fiber dust. Guinea pigs, cats, rats and mice were employed in this inhalation experiment. UPATIONAL MEDICINE 1 animals that had inhaled the fliculty of completely eliminatasbestos as required for an -sue reaction after the animals 1 in this experim ent but not in offered : W hen the reaction is osure, the contraction of the iat may have occurred; in this )bserved was less mature, its parent. s D ust JO per cent ball-milled asbestos tissue reaction in comparison hypothesis that short fibers of lie etiology of asbestosis was directed^ to the view that the in that etiology. The K ing's experiment had a rather low d considerable serpentine and d to conduct a new inhalation which would be richer in long / the Dust.--The dusting material om an asbestos fabricating plant. >s dust were first submitted to the these, which was low in magnetite ted to be about 75 per cent, was fastened to the inside surface of e preceding inhalation experiment, and liberate more fibers into the used is indicated by the chemical nd 3. Analysis of air-suspended 60 per cent of the long fiber dust : as already noted, the composition short fiber dust was 15 per cent er samples taken inside the animal >r the experiments with short filter -eperiment with long fiber asbestos lion particles per cubic foot of a ir; ear, 39 million, and for the fourth I of the long fiber asbestos dust 11. Both samples were collected noted that there was far more ved in this inhalation experiment. VORWALD ET A L .S T U D I E S OF ASBESTOSIS 23 Reaction in Guinea Pigs.--The experiment was started with 100 guinea pigs. After exposure had been carried on for a year, a severe epidemic of pneumonia arose in the dust room and about one third of the animals died or were killed. To replace them, 38 more guinea pigs were added to the surviving group. Histological examination revealed lesions in the lungs after eight months of dust exposure, consisting of cellular connective tissue about the terminal bronchioles (fig. 7 A ). At 12 months there were adenomatoid changes in the adjacent parenchymal areas, and by the sixteenth month (fig. 7 B ) definite fibrosis was present in these areas as well as around the bronchioles. The fibrous lesion could be seen macroscopically at 20 months. From this time on the reaction increased in extent and in the amount of collagen, and by the thirty-fourth month, it had fanned out T able 11.--Size-Frequency of Atmospheric Long Fiber and 100 per Cent BallMilled Asbestos Dust Collected Inside Cages Type of Asbestos ,----------G-r-a-in*-s-,-%---------- ,,------F-i-b-e*r-s-,-%------, < 3 8-10 > 10 <10 > 10 Clumps, Microns Microns Microns Microns Microns % Long ber................... 5.4 1,1 0.0 25.8 6.7 1.0 Ball-milled ................. *0-6 4.8 0.0 0.8 0.6 3.2 Total 100 100 T able 12.--Summary of Inhalation Experiment with Long Fiber Asbestos Dust Nature of Experiment Dust exposure con tinuous throughout life Dust exposure loJlowed by pro longed residence in normal air Animals 117 guinea pigs 4 cats 20 rats 20 mice 12guinea pigs 9 guinea pigs Scats Maximum Maxi Survival mum After Dust Dust Expo Expo sure, sure, Mo. Mo. 36 0 42 0 2 0 25 0 20 14 27 9 18 24 Results Definite fibrosis In 16 mo. Slowly developing fibrosis first seeo a t 24 mo. Marked peribronebiotar fibrosis first seen a t 24 mo. Limited reaction; no fibrosis Clearing of inflammatory reaction and definite contraction of fibrous tissue C'earing of inflammatory reaction and slight contraction of fibrous tissue Similar to continuous exposure group; suggestion of progression in one of tbe two animals considerably into the parenchyma (fig. 8 A ) . The lesions were rather sharply localized and the extensions from different bronchioles showed no tendency to fuse, even in animals exposed for the maximum period of three years. Although the intrapulmonary reaction sometimes reached the pleura, there was no involve ment of that membrane. Emphysema was not detected at any point. Some thicken ing of the larger bronchi with a chronic inflammatory infiltration was revealed, but it was considered no more than would be produced by a similar period of inhalation of any dust. In guinea pigs exposed to the dust for 20 months and then removed to normal air, there was a marked tendency for cellular inflammatory reaction to clear. This effect, accompanied by contraction of the fibrous tissue, resulted in a diminishing size of the focal lesions. None of these animals, killed at various periods up to 14 months after exposure, revealed lesions as large as those in the group killed at the end of the 20 month exposure period or those in animals which remained in the dust room for more than 20 months. Fourteen months after dust exposure ceased. 1he fori in four of the six rem aining guinea pies were so small that thov were In the group exposed for 27 months and then transferred to a normal atmosphere the response was quite similar to that in the 20 month exposure animals mentioned above. Small foci were always visible on gross inspection of sections of all guinea pigs of the 27 month series, but in no instance was there evidence of the reaction. Fig. 7.--Long fiber asbestos inhalation experiment: A , lung of a guinea pig with eight months' dust exposure. The bronchiole at the center already shows an accumulation of phagocytic cells, and there is a slight deposition of collagen. Com pare with figure 6.4, showing the reaction to ball-milled asbestos after 24 months ( X 200). R, lung of a guinea pig with 16 months' dust expbsure. Again note a bronchiole with its surrounding reaction, consisting of fibrosis and adenomatoid change. Col lagen deposition is now seen in the w alls of adjacent alveoli, at the rig h t ( x 200). In the tracheobronchial lymph nodes reaction was first visible at the third month of exposure. By the eighth month patches of cellular connective tissue * l/JW* . H - ---O i O l / i L J u/i . JOULatJ i tVJJw) began to appear in the medulla, and by the fourteenth month most of the node had been replaced by cellular connective tissue. This picture, which resembled that in early silicosis,-persisted to the end of the experiment. Some animals showed, as a variant, heavy sheets of diffusely distributed monocytes and large active giapt cells, but there was never any necrosis or hyaline formation. The spindle-shaped fh ^ i w '4 B i A Fig. 8.--Long fiber asbestos inhalation experiment: A, lung of a guinea pig with 34 months' dust exposure. A bronchiole is seen at the lower center; the large area above it represents the involvement of alveolar walls. Compare with figure 7 B and note the increased extent of reaction (X 200). B , lung of a guinea pig with 20 months' dust exposure and then 14 months' living in normal air. The reaction is essentially like that shown in figure 7 I t : The bronchiole at the right center is surrounded by fibrous tissue with adenomatoid change at the right. There is residual scarring in the walls of adjacent alveoli at the left. It is apparent that no progression has occurred (X 200). new cells were yellowish from fine pigment granules that stained for iron. No fibers or asbostosis bodies were seen. o INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE Although asbcstosis botties were found in the lung as early as one month after exposure began, they were rare and hard to find. At five months more were visible, chiefly coiled inside giant cells, and at eight months many bodies T able 13.--Analyses of Lungs of Guinea Pigs Exposed to Dust in Inhalation Experiment with Long Fiber Asbestos Dust Exposure to Dust, Mo. Period la Norms! Air, Mo. Amt. ot Ash, % ot Dried Lung Total SIOs, % Of Dried Lung Total SIOs, % o t Ash Dust Exposure Continuous During Lite 4.35 0.04 1.10 1 0 - 4.33 0,09 2.11 . 4.3 0.04 0.93 4. 0.05 I 1.23 2 0 4.48 0.06 1.18 4.35 0.06 1.46 4.38 0.06 1.20 8 0 4.38 0.05 1.13 4.51 0.06 1.48 4.77 0.08 1.75 S 0 4.63 0.12 2.67 5.(18 0.09 1.77 4.72 0.10 2.21 8 0 4.92 0.09 1.90 4.34 0.07 1.58 4.87 0.25 5.20 12 0 5J 0.20 4.09 5.16 0.31 5.99 2.98 0.38 12.70 IS 0 2.83 0.35 12.25 ' 3.16 0.34 10.91 3.54 0.43 12.22 20 0 3.60 0.49 13.63 3.58 0.52 14.59 24 0 3.42 8.52 0.35 10.18 0.29 8.29 27 0 3.40 3.74 0.39 11.51 0.49 13.15 3.53 0.87 10.55 30 0 3.03 0.31 11.22 8.88 0.24 6.10 34 0 5.85 OSO 8.60 8.70 0.84 12.47 86 0 4.10 037 9.11 2.74 0.35 12.89 Dust Exposure Followed by Prolonged Residence In Normal Air 3.54 0.43 12.23 20 0 3.60 0.49 ; 13.63 3.58 0.52 14.59 20 4 2.92 0.21 7.23 231 0.27 9.60 20 4.18 0.24 5.78 4.30 0.22 5.07 20 14 5.01 0.21 '4.19 5.04 0.18 3.56 I 3.40 0.39 11.51 27 O1l 3.74 0.49 13.15 27 S 3.5 0.31 2.54 0.18 8.59 6.94 27 7 3.19 / 0.25 3.18 0.28 7.99 8.72 27 3.21 0.29 8.96 2.75 0.23 8.31 Tissue Reaction * 0 + + 2+ 2+ 3+ 3+ 4+ 4+ 4+ 2+ 2+ + + 8+ 2+ *+ + * The symbols averaging the tissue reaction In each group represent merely the relative degree o t reaction, ranging from o to (questionable) to 4+ (the maximum to r this experi ment). The relationships apply only within this table and cannot be compared with symbols In other tables. I - were free in connective tissue. They became fairly abundant as exposure con tinued, although in some later animals the asbestosis bodies were only moderately numerous. It is important to note from analyses of the lungs (table 13) that even though the tissue response at any given period of time was much greater in the guinea i VORWALD E pigs of this experiment tha: asbestos, the amount of mini Reaction in Cats.--Four 14, 25, 33 and 42 months, r cats, after being exposed to an additional 24 months, i cellular accumulations of p1 arterioles together with com; lymph nodes. A t that time pointed, yellow fibers were : months, reaction in the local nective tissue which made > and arterioles, marked lymphs walls (fig. 9 ). Typical asl Fig. 9.--Long fiber asbesti months' dust exposure. Two l> and collagen deposition ( X 200 an occasional fiber, smooth, yi reaction was similar in location slower in development. Roetv 25, 33 and 42 months, respecti' lesions. Reaction in Rats.--Althougl from pneumonia and were not ? exposed for 19 months and four a n d offered a basis for tentative was just beginning. All four peribronchiolar fibrosis. After bodies were found in the 19 mi animal. Thus these animals exl accompanied by only a very infri VORWALD ET AL.--STUDIES OF ASBEST0S1S 27 pigs of this experiment than in those exposed to either short fiber or ball-milled asbestos, the amount of mineral matter in the lung ash was much less. Reaction in Cats.--Four cats inhaled the long fiber asbestos dust for periods of 14, 25, 33 and 42 months, respectively, and were immediately killed. Two other cats, after being exposed to dust for 18 months, lived in a normal atmosphere for an additional 24 months. Fourteen months' exposure was sufficient to produce cellular accumulations of phagocytes around terminal bronchioles and peripheral arterioles together with compact collections of similar cells in the tracheobronchial lymph nodes. At that time there were no typical asbestosis bodies, but smooth, pointed, yellow fibers were seen very rarely. With continued exposure, up to 42 months, reaction in the locations noted progressed to the formation of cellular con nective tissue which made well defined sheaths about the respiratory bronchioles and arterioles, marked lymphoid hyperplasia and lymphoid infiltration of bronchiolar walls (fig. 9). Typical asbestosis bodies were not formed, although there was Fig. 9.--Long fiber asbestos inhalation experiment: Lung of a cat with 42 months' dust exposure. Two bronchioles are shown with adjacent cellular reaction and collagen deposition (X 200). an occasional fiber, smooth, yellow and pointed. Pleurisy was not present The reaction was similar in location to that in the guinea pigs, but fibrosis was much slower in development. Roentgenograms of cats made after exposure periods of 25, 33 and 42 months, respectively, failed to demonstrate evidence of pulmonary lesions. Reaction in Rats.--Although 20 rats were placed in the dust room, many died from pneumonia and were not suitable for study. Five animals, of which one was exposed for 19 months and four for 25 months, were free from pulmonary infection and offered a basis for tentative conclusions. In the 19 month animat, the reaction was just beginning. All four animats killed at 25 months showed a well marked peribronchiolar fibrosis. After a long search, only two small, smooth asbestosis bodies were found in the 19 month animal and none was found in the 25 month animat. T hus these animals exhibited fibrosis without asbestosis bodies'or fibrosis accompanied by only a very infrequent asbestosis body. AS INDUSTRIAL HYGIENE AND OCCUPATIONAL. MEDICINE Reaction in Mice.-- O u t of 20 w hite m ice used in this experim ent, 11 lived a y ear o r m ore in dust and died o r w ere killed w ithout show ing an appreciable degree of pulm onary infection. T he reaction to the inhaled dust was lim ited to phago cytosis by mononuclear cells. U sually these w ere widely scattered through the air spaces; a limited num ber were grouped about the term inal bronchioles, producing some thickening of their walls. T here was no suggestion of fibrosis. Num erous asbestosis bodies w ere observed in anim als killed late in the experi ment. Thus these anim als exhibited asbestosis bodies without fibrosis. Sum m ary and Interpretation oj Inhalation Experim ent with Long Fiber A sbestos D ust.-- T he purpose of this experim ent was to evaluate the importance of long fibers in the tissue response to inhaled asbestos. T he results, in com parison w ith those of previous investigations, indicate strongly that long fibers are chiefly responsible for asbestosis. Thus, the reaction in guinea pigs developed earlier and became more extensive in this experiment than in previous experiments in spite of a smaller concentration of atmospheric dust and a lower mineral content of the lungs. F urtherm ore, typical peribronchiolar fibrosis was produced in cats, although in a previous experiment with short fiber dust peribron chiolar fibrosis did not develop in this species. T he cause of the cellular fibrosis in the lymph nodes of the guinea pigs is not clear. It did not occur in other inhalation experim ents with asbestos. INJECTION EXPERIMENTS Since the inhalation experiments reported above strongly suggested that long fibers of asbestos are the significant factor in the causation of asbestosis, a series of injection experiments was inaugurated wherein the dosage and the length of the fibers could be controlled more precisely. Also, by the use of controlled dosages, the relative capacities of various asbestos minerals to produce reaction could be compared. In these injection experiments, guinea pigs, rabbits, rats and dogs were used, and the mineral dust was injected by the intratracheal, the intraperitoneal and the intravenous technic, but not all the technics w ere used for each species. F o r the purpose of simplification the findings in each series of tests, except for dogs, have been condensed and reported in tables, to which reference will be made later. In the case of dogs, only one test was made, and since the findings were negative, no detailed report is included. * E xperiments U sing I ntratracheal T echnic A s the asbestos m inerals do not cause typical advanced fibrosis in extrapulm onary tissue, the intratracheal technic is the preferred way of introducing fibrous dust into the experimental animal. In this method the dust suspension is injected by means of a special needle o r catheter deep into the trachea, from which it flows into the lungs. Comparison o f F ibrous and N o n fibrous D usts.-- T o dem onstrate that the ability of asbestos to produce fibrosis resides in its fibrous character, the series of injection experim ents reported in table 14 w ere performed. T able 14.--Comparison of Peat Dosage: Each animal was given an int of the dust. Two weeks later soothe injected was 50 me. Animals used: Six groups of 0 guinea , Periods a t which animals were killed: 1 months after la s t injection. Preparation of dust: Cbrysotile (bait reground in agate m ortar. Chrysotfle (ball milled) ignited: Ball i ground in agate m ortar 2 or 3 min. t'hrysotlle (fibrous) unheated: (round Chrysolite (fibrous) ignited: 200-mesh i grinding. Serpentine (ball milled) unheated: Bail Serpentine (ball milled) ignited: Ball r ground in agate m ortar 2 or 3 min. Mineral Chrysotile (hall milled) unheated Chrysotile (ball milled) ignited Chysotile (fibrous) unheated Chrysolite (fibrous) Ignited Serpentine (ball milled) unheated Serpentine (ball milled) Ignited Size of Dust Particles 3 microns and less 3 microns and less Grind COI tioolr at ph th> eh: br( Rcai pn 20-50 microns approx. 20-50 microns approx. 3 microns and less 3 microns and less A diet ab< Oot spa Re new sbi. In; at : occt rear and tlor that' tlssi react vlel: tlgftl aettAsl well mat tort with trap curwall React I prol: brltt rear Dust r eyto excelSligtl pnci Dust for ' tend T a b le 14.--Comparison of Reactions to Chrysotile and Serpentine Injected Intratracheally Dosage: Each animal was given an intratracheal injection of 0.5 cc. of a 5 per cent suspension o t the dust. Two weeks later another similar injection was given. T o tal am ount of dust injected was 50 mg. Animals used: Six groups of 9 guinea pigs each (one group for each type of dust). Periods a t which animals were killed: One o r two animals in each group a t 1, 2, 6, 8% and 12 months attar last injection. Preparation o t dust: Chrysotile (ball milled) unheated: Ball milled for 1,176 hr., dried and reground in agate m ortar. Chrysotile (ball milled) ignited: Ball milted chrysotiie heated for 2 hr. a t ab o u t 700 C., then ground in agate m o rtar 2 or 3 min. Chrysotile (fibrous) unheated: Ground in agate m o rtar to pass 200 mesh. Chrysotile (fibrous) ignited: 200-mesh m aterial heated for 2 hr. at about 700 C. No further grinding. Serpentine (ball milled) unheated: Ball milled for 1,488 hr., dried and regronnd in agate m ortar. Serpentine (ball milled) Ignited: Ball milled serpentine heated for 2 hr. a t ab o u t 700 C., then ground in agate m ortar 2 or 3 min. Mineral Chrysotile (hall milled) unheated Chrysotile (ball milled) ignited Chysotlle (fibrous) . unheated Chrysotile (fibrous) Ignited Serpentine (ball milled) unheated Serpentine (ball milled) ignited Si2e o t Dust Particles 3 microns and less 3 microns and less Results Grinding destroyed capacity to cause fibrosis. At l mo. considerable inflammatory edema and cellular prolifora* tion and localization of dust particles ab o u t bronchi* oles; a t 2 mo., only a very slight proliferative reaction; at 0, S h i and 12 mo., widely scattered small mononuclear phagocytes. A t 12 mo., a lew microscopic patches of thin alveolar wall thickening with some adenomatoid change In portion of air spaces ab u ttin g on thickened bronchi. No asbestosis bodies seen. Reaction limited to large foreign body g ian t cells without production of fibrous tissue. 20*50 microns approx. 20*50 microns approx. 3 microns and 3 microns and less A distinct fibrosis. Reaction localized to connective tissue about terminal bronchioles; little within those tubes. Contraction caused adenomatoid appearance of air spaces given off directly from terminal bronchioles. Reaction area became smaller with progress of time: no new regions involved. No chronic pleurisy even a t polots abutting intrapulmonary change. At l mo. considerable Inflammatory edema and foci of cellular proliferation; a t 2 mo. well marked cellular proliferation and fibrosis occurring locally about respiratory bronchioles. This reaction developed before asbestosis bodies had formed and was as advanced as th a t produced by 2 yr. inhala tion of asbestos dust. At 6 mo., reaction less extensive than a t 2 mo., apparently due to contraction of fibrous tissue; asbestosis bodies were abundant. A t 8% mo., reaction still less extensive, confined to the immediate vicinity of the small terminal bronchioles, where the scar tissue was quite dense and was becoming hyaline Id char* actcr. Sometimes it even obliterated th e bronchiole. Asbestosis bodies had become scarce. A t 12 mo., the well developed peribronchial and intrabronchlal adenoi m atoid areas of fibrosis had produced considerable dis tortion. More peripherally were patches of pneumonitis with eosinophilic Infiltration, some of which was being transform ed into fibrous tissue. These seemed to be pre cursors of the localized, diffuse patches o t thin alveolar wall fibrosis seen elsewhere. Reaction limited to large foreign body g ian t cells without proliferation. H eating the fibers, which made them brittle, destroyed their capacity to produce significant reaction. Dust relatively Inactive. At 1 and 2 mo., simple phago cytosis without proliferation; at G mo., no change except possibly lymphoid cell Infiltration; a t 8% mo., a slight chronic pneumonitis: a t 12 mo., only a little pneumonitis w ithout suggestion of fibrosis. Dust relatively Inactive. Reaction essentially the same as for unheated serpentine. With ignited serpentine, less tendency for dust to be carried to bronchial nodes. U INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE I VORWALD E The tests were made \ chrysotile that had been milled to reduce the lenj. time control tests wen chemical composition as findings reveals that on) typical peribronchiolar l only fibers less than 3 i 10 and 11). Fibers su to cause serious tissue in the chrysotile fibers, from a flexible to a brittl t F*K- 10.--Comparison of reactions provoked by injected long fiber and ballmilled asbestos dusts: A , lung of a guinea pig which four months before had received an intratracheal injection of long fiber asbestos dust. Note the peri bronchiolar accumulation of cells with collagen deposition. The bronchiole chiefly involved is in the midst of the reaction ( x 200). , . B,\ung of a guinea pig which four months before had received an intratracheal injection of ball-milled asbestos dust A bronchiole is shown at the right. In contrast with A, note that only a few cells have accumulated about the bronchiole and that collagen deposition is absent ( x 200). i t i is shown at the left center the bronchiole and collagen mental studies concernim> publication. Comparison of Vario findings are disclosed by 15. First, all the long fil of anthophyllite, prodw broncliiolar reaction can minerals--chrysotile, anv and 12. Why anthophyl minerals is not entirely < Second, with the mi fibrous form of magne VORWALD E T AL.--StVD i'E S OF ASBESTOSIS 31 T h e tests w ere m ade w ith long fiber chrysotile, unheated, and w ith chrysotile that had been ignited to destroy its flexible stru ctu re o r ball m illed to reduce the length of fiber to 3 m icrons and less. A t the sam e tim e control tests w ere m ade w ith serpentine, which has the same chemical com position as chrysotile but is nonfibrous. A review of th e findings reveals that only the unheated, long fiber chrysotile produced typical peribronchiolar fibrosis and that ball-m illed m aterial containing only fibers less than 3 m icrons in length failed to cause fibrosis (figs. 10 and 11). Fibers subjected to ignition also had lost their capacity to cause serious tissue dam age. Ignition produced im portant changes in the chrysotile fibers, am ong them being loss of w ater, an alteration from a flexible to a brittle stru ctu re and possibly o th er changes. E x p eri m ental studies concerning this observation will be reported in a separate publication. Comparison of Various Long Fiber Dusts.-- S o m e v e ry in te re stin g findings are disclosed by the resu lts of the ex p erim en ts recorded in table 15. F irst, all the long fiber asb esto s m in erals tested , w ith th e exception of anthophyllite, produced typical fibrosis. T h e characteristic peri bronchiolar reaction caused b y th ree representative long fiber asbestos m inerals-- chrysotile, am osite and crocidolite-- is show n in figures 10 A a n d 12. W hy anthophyllite behaved d ifferen tly from th e o th er asbestos m inerals is not entirely clear. Second, w ith the m ineral brucite, w hich is n o t a silicate but is a fibrous form of m agnesium h y d ro x id e, a ch aracteristic fibrosis like / K'if L o t u j l i c r D u sts i n j e c t e d Intratrachcady Dosage: Two injections of 0 3 cc. o f a 5 per cent suspension given two weeks ap a rt. T otal dose w as 50 mg. Animals used: From 6 to 9 guinea pigs for each dust. P eriods a t which anim als were killed: Usually a t 1, 4, 8 aod 12 m onths a fte r la s t injection. Size o f d u st particles: S eparated so th a t m ost fibers were from 20 to 50 microns long. Mineral O h ry so tile (Thetlord) ChrysotUe (Arizona: lowiron eontent, 0.2% FesOa) Amoelte CrocldoUte (Bolivia) Oroeidolite (8. Africa) Anthophylllte Tremolile Bruche Glass wool Results Distinct fibrosis. Additional inform ation given opposite cbrysotlle (fibrous) unheated, in table 14. Reaction virtually identical with th a t to Thetford ohrysotile. Both fibrosis aud asbestosis lu>dics produced w ith an asto sto s containing very little iron. Fibrosis occurred as plugs w ithin term inal bronchioles and as finer deposits a t periphery. Fibrosis developed before asbestosis bodies were seen and was in cellular sta te well formed u t one m onth. W ith age. fibrous tissue contracted and occupied smaller area but was more dense. Adenomatoid changes similar to those with Thetford ehrysotlle. Pleurisy limited to Iminedlutc vicinity of early reaction about areas of massive localization. Asbestosis bodies formed but were few. A t 1 mo. after injection, minute foci of mononuclear proliferation about bronchioles and in areas of atelectasis: a t 1% mo., heavy peribronchiolar patches of fibrosis often with papillary projections partially closing lumen of bronchiole; adenomatoid appearance marked; connective tissue reaction showed heavy collagen but no hyaiinizution: a t 2 mo., m inute foci of well m atured fibrosis ab o u t bronchioles;' a t 6 m o., m ature asbestosis fibrosis with evidence of contraction; considerable chronic pneumonitis with infiltration of lymphocytes and eosinophils. At 9 mo., small intrabronchiolar fibrous plugs with foci of more delicate fibrosis a t periphery. Typical fibrous endobronohlolitls and peribronchiolitis with form ation of atypical asbestosis bodies. H austration of bodies began before 4th mo. a fte r injection, well developed by sth mo. Bodies persist afte r 12th mo. Reaction at i mo. heavy endobronchlolitls and peribronchiolitis already showing fibrous changes; atelectasis and fibrosis with some necrosis at site of massive localization of dust. At 4 mo., heavy, widely scattered endobronehiolitts and peribronchiolitis, now fibrous, with marked defor m ity of bronchioles and with an adenom atoid appearance. At 8 and 10% mo., reaction in lung essentially the same as a t 4 mo. A t 12 mo., foci of fibrous endobronchiolttis and peribronchiolitis still large, with more dense sear tissue and m ore deform ity of bronchial tubes but no extension into, or atelectasis of, peripheral parenchyma. ^ Advanced fibrous endobronchlolitls and peribronchiolitis. Beaded asbes tosis bodies noted a t 8 mo. A t 1 mo., early fibrous endobronchiolitig and peribronchiolitis: m ao y g ia n t cells and some lymphocytic reaction. A t 4 m o., small areas o f endohronchiolitis scattered throughout the lung: cellular fibrosis. At 8 and 12 mo., areas of bronchiolitis sm aller bceause of cootraetion o f dense scar tissue; a t 12 mo., m arked lymphocytic infil tration and adenomatoid appearnnee. Typical advanced fibrous endohronchiolitis and peribronchiolitis produced by 0.5% suspension (1 ce. to ta l dose); m ost anim als would n o t tolerate usual 5% suspension. Fibrosis well developed before asbestosis bodies seen. At 4 mo., well developed fibrous bronchiolitis w ith lymphocytes and g ia n t cells and adenom atoid change. A t $ mo., typical bronchiolitis n o t quite as extensive o r a s heavily fibrous as with a 5% suspension, other wise the same. Many deeply stained fitters with a good proportion of h au stra te d asbestosis bodies. At 12 mo., heavy fibrous bronchiolitis, more peribronchiolitis and endobronchlolitls, with lymphocytes and giant cells: very m arked adenom atoid appearance. Lymphocytic Infiltration and g ia n t cells b u t no fibrosis. A very few atypical asbestosis bodies. A t X m o., m any scattered foci of intrabronchiolar dust w ithout massive localization; lymphocytic infiltration of walls and a few g ia n t cells. A t 8 an d 12 m o., little evidence o f d u st: a few bronchioles and bronchi with g ia n t cells in adjacent alveoli and with lymphocytic infiltration of walls. Fibrosis about bronchioles. A t 1 mo., areas of dust localization with col lapse o f alveoli and infiltration w ith a ru te Inflam m atory cells, m acro phages and g ia n t cells. W ithin th e area were a few foci o f fibrous tissue and numerous areas o f hypertrophy of alveolar epithelium. Many bron chioles packed with fibers. A t 4 mo., general appearance of lesion unchanged: pleura slightly thickened over heavy localizations of dust. An occasional segmented asbestosis body seen. At s mo., m any foci of fibers in bronchioles and alveolar duets with cellular reaction as before: also, soim* foci showed d istin ct collagen deposition. At 12 and 18 mo., reaction as before with fibrosis about bronchioles more apparent because of con traction and decrease o f inflam m ation. Giant cells prominent. Fleura markedly involved. . Typical fibrous eodobronehtolitts and peribronchiolitis like reaction to asbestos m inerals. A t 1 m o., extensive endohronehloMtl* and peribron chiolitis with giant cells: dense fibrous loops within bronchioles and cellu la r fibrosis about them : adenom atoid change present. At 2 mo., heavy intrabronchiolar and peribronchiolar fibrosis producing marked deformity with distortion o f tubes and obliteration of surrounding air spaces: fibrosis pale w ithout hyalinisation b u t with few nuclei: no necrosis. Typi cal asbestosis bodies seen. A t 4 and a mo.. Httie change; fibrous tissue contracting. At 10% m o., dense fibrous bronchiolitis with asbestosis bodies. Ko pleurisy. Ko extension to surrounding lung. Ko fibrosis within a year. A t 1 m o., no reaction Inside bronchioles; in peripheral a ir spaces clumps o f g ia n t cells pocked with fine spicules of glass with lymphocytic infiltration of adjacent walls: no asbestosis bodies. At 2 mo., reaction less Intense th a n a t l m o.: fair-sized clump of don VORWALD ET . that produced by the asbesto the brucite used contained o obvious that a siliceous coi development of asbestosis. H g . 12.-- A m o site and crocido' pig four m ouths after an intratr; reaction exhibits pronounced accun B , lung o f a guinea pig four m \ lite- A s in A , peribronchiolar acc shown ( X 200). Third, no fibrosis resulte< (fig. 13 B ) t even though glas 4 VORWALD ET AL.--STUDIES OF ASBEST0S1S 33 that produced by the asbestos minerals was obtained (fig. 13 A ). Since the brucite used contained only 0.90 per cent silica as an impurity, it is obvious that a siliceous component is not an essential factor in the development of asbestosis. F ig. 12.--Am ositc and crocidolite injection ex p erim ents: A, lung of a guinea pig four months after an intratracheal injection of amosite. The inflammatory reaction exhibits pronounced accumulation of cells and collagen deposition (X 200). B, lung o f a guinea pig fo u r m onths a fte r an in tratrach eal injection of crocido lite. A s in A, peribronchiolar accumulation of cells and deposition of collagen are shown (X 200). Third, no fibrosis resulted from the injection of glass wool fibers (fig. 13 B), even though glass wool resembles asbestos in many ways. J-* VU U I K I A L H H j l h i \ E AND OCCUPATIONAL MEDICINE in diameter is a solid rod which in short lengths is fairly rigid, while an asbestos fiber of the same diameter is a bundle of extremely fine filaments which impart to the fiber a high degree of flexibility. It would seem that this structure and the associated flexibility are important factors governing the capacity of a mineral to produce peribronchiolar F fo 13.--Brucite and glass wool injection experiments: A , lung of a guinea pig which four months before had received an intratracheal injection of brucite. Even with this nonsiliceous fibrous mineral there is peribronchiolar accumulation of cells and deposition of collagen similar to that shown in A and B of figure 12 ( X 200). _B, lung of a guinea pig which four months before had received an intratracheal injection of glass wool. Two bronchioles are shown, one in cross section and the other in longitudinal section. Below the latter is a thick-walled blood vessel. The bronchioles are without reaction and can be considered normal for comparison with other figures. Glass wool fibers are present in this field but cannot be seen at this magnification (X 200). VORWALD ET fibrosis. Experimental si reported in a separate public T able 16.--Comparison of /?. Dusii Dosage: Two Injections ot O.S ce. dose was SO mg. Animals used: Six groups ot gutnei Periods at wblcb animals were itlllei Mineral Size of Dust Particles Chrysottle (Thetford) Amoslte Long fiber, 20-50 microns Short fiber, 3 microns and less Long fiber, 20-50 microns Short fiber, 20 microns and less Crocidollte (Bolivia) Long fiber, 20-50 microns Short fiber, 20 microns and less AntbopbyDIte Long fiber, 20-50 microns Short fiber, 3 microns and less \ Tremollte Long fiber, 20-50 microns Short fiber, 20 microns and less Brucite \ Long fiber, 1 20-50 microns Short fiber I (made by crushing long fibers with rubber police man) Compari.inn of T ono Fib VORWALD ET AL.--STUDIES OF ASBESTOSIS 35 fibrosis! Experimental studies concerning this observation will be reported in a separate publication. T able 16.--Comparison of Reactions Produced by Long F iber and S h o rt Fiber Dusts Injected Intratracheally Dosage: Two injections of 0.6 cc. o f a 6 per cent suspension given tw o weeks ap a rt. dose was 50 mg. Animals used: Six groups of guinea pigs. Periods a t which animals were killed: 1, 2, 6, 8% and 12 m onths afte r injection. Total Mineral Size of Dust Particles Results Uhrysotile (Thetford) L ong fiber, 20*50 microns Short fiber, 3 microns and less A distinct fibrosis. Refer to chrysotUe (fibrous) un heated in table 14. No fibrosis. Refer to ebrysotile (ball milled) unheated in table 14. AroosJte L ong fiber, 20-50 microns S hort fiber, 20 microns and less Typical fibrous endobronebiolitis and peribronchiolitis. Refer to table 15. Reaction limited to phagocytosis with lymphocytic infil tration of adjacent walls. Short fibers packed inside swollen phagocytes: longer ones free; some coated to form typical asbestosis bodies. At 1 mo. after Injec tion, alveoli contained good-sized g ia n t cells, m ost phagocytes were within air spaces and had n o t m igrated to walls. At 4 mo., free extracellular fibers had worked themselves into interstitial tissue, where there was extensive proliferation of lymphoid cells and monocytes but no fibrosis. At 8 mo. foreign body reaction with some pneumonitis, no bronchiolitis. Typical asbestosis bodies present. Crocidolite (Bolivia) Long fiber, 20-50 microns Advanced fibrous endobronebiolitis and peribronchio litis. Refer to table 15. S hort fiber, 20 microns No fibrosis. At l mo., air spaces compressed and largely filled with g ian t cells packed with d u st needles. and less Walls heavily Infiltrated with monocytes and lymph oid cells. A t 4 mo., a m oderate degree o f cellular infiltration of walls; small g ia n t cells packed with dust spicules. A t 6 an d 8 % m o., masses o f g ian t cells, containing mineral particles, in small bronchi but n o t in respiratory bronchioles; sm aller ones widely scat tered In terminal air spaces. Numerous asbestosis bodies. No reaction to connective tissue. No endo bronchial proliferation. A t 12 m o., m any scattered small monocytes packed with dust. No endobronchitls. No peripheral fibrosis. In lymph node, slight reticulosis; no fibrosis. Anthopbyllite V Long fiber, 20-50 microns S hort fiber, 3 microns and less Lymphocytic infiltration and g ia n t cells b u t no definite fibrosis. Refer to table 15. No fibrosis and practically no asbestosis bodies. A t 1 mo., focal collections of dust-filled monocytes and a few giant cells; a t 4 mo., some adenom atoid epithelial reaction; a t 8 mo., simple pneumonitis with phago cytosis of short fibers; a t 12 mo., isolated and sharply localized collections o f d u st cells Inside a ir spaces about terminal arterioles. Reaction in walls limited to lymphoid cell infiltration. No fibrosis. In lymph node, reaction limited to slight prominence of reticu-: lum. Tremoli te L ong fiber, 20-50 microns S hort fiber, 20 microns Fibrosis about bronchioles. Refer to tab le 15. Simple foreign body reaction. No acute Inflammation. No accumulation of d u st In o r ab o u t term inal bron and less chioles. No eodobronchitls. A t 1 m o., scattered small giant cells and considerable infiltration o f adjacent wans with monocytes and lymphoid cells. A t 4 mo., little change except more cellular Infiltration of con nective tissue. At 8 mo., lymphoid Infiltration and thickening of walls about some b u t n o t all terminal bronchioles. Brucite \ Long fiber, 20-50 microns S hort fiber (made by crashing long fibers with rubber police man) Typical fibrous endobronebiolitis and peribronchiolitis like reaction to asbestos minerals. Refer to table 15. Inert type of reaction. At 1 mo. after injection, small monocytes widely scattered through a ir spaces; focus of atelectasis with lymphoid Infiltration of compressed air-space walls. No endobronchial reaction a s with chrysotUe. At 2 mo., reaction sim ilar to th a t a t l mo.; typical asbestosis bodies seen. A t 12 m o., small clumps of loactive dust-filled phagocytes; no fibrosis. No reaction in lymph nodes. C o m p a riso n o f J.nnn F ih rr m id S h o rt F iber D v s f x -- W itli nnort-r T able 17.--Summary of Injection Experiments by Intravenous Technic 36 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE intense is the tissue reaction and that particles larger than 3 microns in diameter cause little reaction. In the case of asbestos, however, the reverse is true and apparently only long fibers have any specific effect, as was suggested by the inhalation experiments. This is confirmed by the data of table 16, in which a series of tests with fibrous minerals is reported. When the injected dust consisted of fibers 20 to 50 microns long, all the fibrous minerals tested except anthophyllite, as noted in the preceding section, produced fibrosis; when the material was prepared by first grinding the fibrous dust until the length of fibers was reduced to 20 microns and less or, in some cases, to 3 microns and less, none of the injected dusts caused fibrosis. These results differ from those of King, Clegg and Rae,u who reported the production of reticulosis comparable to the experimental silicotic nodule in rabbits receiving monthly intratracheal injections of 100 mg. of Rhodesian asbestos fibers, 15 microns long, and the produc tion of diffuse interstitial fibrosis in rabbits receiving similar injections of short fibers, 2.5 microns in length. We believe this dose, especially in the long term rabbits, is highly excessive. In our experiments the dosage was kept low in order to minimize untoward reactions which might obscure the peribronchiolar type of fibrosis which characterizes early human asbestosis. E xperiments U sing I ntravenous T echnic The experiments summarized in table 17, in which the intravenous method of injection was employed, show that the asbestos minerals are far different from quartz in their action on tissue. It has been repeatedly demonstrated that intravenous injection of quartz particles 3 microns and less in diameter will cause a typical tissue reaction with the development of hyalinized fibrotic lesions in extrapulmonary sites, such as the liver and the spleen. Asbestos minerals, however, on intravenous injection generally produce only an inert type of reaction, as is revealed by the results given in the table. The reason for the early deaths in the experiment with chrysotile particles is not clear. E xperiments U sing I ntraperitoneal T echnic The results of injection experiments with the intraperitoneal technic are given in table 18. It will be noted that the long fiber dusts produced a fibrous reaction while dusts composed of particles 3 microns and less in size caused only an inert type of response. These experiments indi cate also that the fibrosis initiated by the irritation of asbestos fibers is not restricted to the lungs, as was formerly assumed, but can be pro duced in the peritoneum as well. OTHER EXPERIMENTS W ITH ASBESTOS MINERALS A number of additional experiments were conducted to throw more light on specific phases of the asbestosis problem.1 11. King, E. J . ; Clegg, J. W., amt Rae, V. M.: Effect of Asbestos, and of -I.,,! M ',m i n i m i mi T i i ` i<> I * - . U . i t , - Tin ,r*i i- 1 1eQ mil- . .,1 ....... T a b le 17.--Summary of Injection Experiments by Intravenous Technic D osage: T o ta l am o u n t o f d u s t w as 1.0 Gm., divided in to 20 equal doses (each dose w as 5 cc. o t a 1 per cent suspension) which were given twice a week fo r 10 weeks. Mineral Chrysotfle (Thetford) Amosite Crocidoltte Anthophyllfte T rem ollte (soda-iron) Tremolite (soda) Size of Dust Particles 3 microns and less (hall milled 132 hr.) 3 microns and less (g ro u n d In agate m ortar) 3 microns and less (ground in agate m ortar) 3 microns and less (hall milled 1,400 hr.) 3 microns and less (hail milled 140 hr.) 3 microns an d loss (hall milled 4$ hr.) R a b b its Used 6 & 4 4 4 4 M axim um Survival After Last Injection, Mo. 17 72 24 19 24 Results The ra b b its did n o t to le ra te Intravenous injections o l finely ground chrysotlle an d 5 o f the 3 died a fte r 1 to 5 injections o f even diluted suspensions; th e o th e r anim al died a fte r 27 injections o f one* q u a rte r stre n g th suspension (GOd a y s a fte r first in jection). Reaction lim ited to few la rg e g ia n t p h ag o cytes o f inactive type in liver, spleen an d lungs. No throm bi o f d u st cells seen in pulm ooary capil laries. No definite explanation lo r fatalities discovered, b u t m aterial m ay have been retained in heart, causing local throm bi. .Advanced pu lm o n ary infection killed 3 an im als a t 9, 11 an d 17 m o. a f te r la s t in jectio n , sho rten in g Intended d u ratio n o t experim ent and com plicating picture. However, ra b b its killed earlier (3 and 3 m o.) showed only Inert phagocytosis w ith n o progression in th e 6 mo. an im al. T h e la s t tw o (11 an d 17 m o.) were p ro b ab ly th e sam e alth o u g h lo c al necrosis of th e liver an d am yloid o f th e spleen made Interpretation difficult. R eaction w as th a t to a n in ert substance w ith n o change In 12 m o. (O ther o b serv atio n s a t 3, 4 an d 3 mo.) Simple phagocytosis of particles. No tendency to agglom erate and no change In adjacent tissues. Grinding the d u st to sizes o f 3 microns and under destroyed th e fibrous stru ctu re o f this m ineral, and th e injected m aterial resembled plates rath e r th an fibers. R eaction essentially t h a t o f an in e rt m ineral. O bservations m ade a t 3, 6, 12 an d 24 m o . Only sugges tio n o f irrita tin g p ro p erties m anifested in spleen an d lym ph nodes, b u t n o t liver, of th e 24 m o. rab b it. In this anim al there had been proliferation o f mononuclear and g ia n t cells th a t w as n o t p resen t in eith er spleen o r lym ph node o f 12 m o. anim al. T he absence o f associated fibroblastic reaction in these o rg an s and o f any change in the liver condition justifies th e classification of anthophylllte a s an inert silicate. No fibers were retained In lung to d em o n strate whether asbestosis bodies would develop. Reaction essentially th a t of an Inert m ineral. L ast anim al killed showed a little proliferation and lym phocytic in filtratio n in liver, n o t seen earlier ( a t 3, 3 and 12 m o.). No evidence o f an y a c tiv ity in lesions in other organs. An in ert foreign body reactio n w ith n o change in 24 m o. O bservations m ade a t 3, 0, 12 and 24 mo. T a ble 18.--S um m ary o f In jection E xperim ents b y Intraperitoneal Technic Dosage: Each anim al# received a single Intraperitoneal Injection o f 2 cc. o f a 10 per cent dust suspension. T otal am ount o f du st Injected was 0.3 Gm. Mineral ChrysotUe (Thetford) Cbrysotile (Thetford) Amosite Crocidolite Anthophyllite Anthophyllite (originally labeled talc) Tremolite (soda-iron) Tremolite (soda) Anthophyllite Pyrophyllite (fibrous) Pyrophyllite (crystalline) Size of Dust Particles Guinea Pigs Used 8 microns and less 16 (ball milled 216 h r .) ------ Maximum Survival A lter Injection, Mo. 36 Long fiber 4 2 (through lOOmesb) 3 microns and less 0 12 (ground in agate mortar) 3 microns and less; 7 12 also some long spicules (ground in agate m ortar) 3 microns and less 5 25 (ball milled 1,400 hr.) Mostly 3 microns 5 12 and less; some fibers 30 microns or more long (ground in agate mortar) 3 microns and less 5 12 (ball milled 15 hr.) 3 microns and less 6 18 (ball milled 48 hr.) 100 microns and less 100 microns and less 100 microns and leu 6 12 6 12 6 12 Results No fibrosis o r asbestosls bodies. D ust particles ingested by phagocytes, chiefly multlnudeated variety. Six mo. alter injection fibrous elements of d u st appear to have dissolved leaving only the Insoluble magnetite, a contaminant. No reaction in surrounding 1st o r areolar tissue. No transporting o l dust to regional lymph nodes. Observations made a t Intervals from 1 to 36 mo. alter injection. Definite fibrous reaction produced, delicate and nonhyaline. Atypical asbestosls bodies developed, b u t all were unusually small. No evidence o l ex tra long fibers seen. Observations only a t 2 mo. Inlection interfered with interpretation. Dust reaction appeared to be o l inert type and limited to phagocytosis with a moderate tendency to lymphocytic Infiltration. Observations a t 1, 4, 8 and 12 mo. Dust loci consisted only ol large mononuclear and giant phagocytes surrounded by a minimum am ount o l cellular connective tissue. The injected d u st contained n o t only fine material th a t in grinding had been mashed Into irregular plates but also many long spicules io microns o r more In length. No asbestosls bodies seen, although the longer spicules appeared slightly swollen and greenish. Observations a t 1, 4, 8 and 12 mo. Essentially inert loreign body reaction. In early animals (1, 4 and 8 mo.) locus of monocytes and small giant cells and a little central necrosis. In th e 4 mo. animal there was also slight peripheral fibrosis. A t 12 and 25 mo., nonprogressive mass o l monocytes and giant cells; no fibrosis. Reaction, which consisted ol very large giant cells surrounded by a variable number o l lympho cytes, was much heavier to these unintentionally long fibers th an to the fine du st in the experiment above. There was more or less proliferation of fibroblasts producing cellular connective tissue visible in areas where the quantity of loreign particles was n o t so great th a t i t obscured the reaction. Observations a t 1, 4, $ and 12 mo. Inert type of response never progressing beyond the stage o f very slight lymphocytic reaction about masses o l dust-filled phagocytes. No fibrosis. Observations a t l, 4, S and 12 mo. In ert nonprogressive foreign body type o f reaction. No fibrosis. Observations a t 1, 4, 8, 12 and 18 mo. Distinct early fibrosis produced by anthophyllite and fibrous pyrophyllite with subsequent regres sion; crystalline pyrophyllite inert throughout. A t 1 mo., g ian t cells about long thick splinters; a t 4 mo., definite fibrosis replacing giant cells o f anthophyllite and fibrous pyrophyllite reaction; a t 8 mo., fibrosis which started a t 4 mo. had decreased, especially with fibrous pyrophyllite. A t 12 mo., reaction to all three dusts consisted of foreign body giant cells with lymphocytes b u t w ithout necrosis o r fibrosis. No asbestosls bodies. * Each animal receiving long fiber chrysottle was given an injection '1 2 ce. of a 0.5 per cent dust suspension. P rotective A c When colloidal aluminui < sW S'* <e3 eco -n 3* < ^ fP* ? CL 1A 1CL s 3ft* S I 9 ITS S.SS i: CL > * 3 ffw 8vo I9 n 3 * 1 53 3<t a?> irt> H< P2 n CL a n as ^ o o a> X 0 *3 p 3 18 r ? o 5* . 3 *0 i-H 1J"V-. (o/> I 8 .8 S 3 3* 3* ~ c ST P r* f 3. 0 3* it ^ ST ** * 5 OfQ V S g t * P 2SS3t. CcOe PST *- P < S ^ o * s g * g . g cr ^ a gf < 3* lJ CO R ? 3 2 . g R w Z n* s * <t et C 3 3 > 2 . | f 3* 3 e g cr 3 2 . cr P p cr 3 3 Q. 32. n tCOt C_ l --* o -n 0* <t co O S' 3 I <*1t n CO P 0; O* OCMOO it . ^ -m* . 0E2L *S- Pco o3rq* CO rt 3ww*e 3 3 w 3 cr 3 3 X w 8 <* 3* <t 8* o orq O. | | 2 , p 3% ^ *3 l.g Me M O 2 t fCOt g 3 <3 S co *3 3 s 3 V * * 3. 5 3 2 w * ~ 2 3-S* O ^ CO <t o M S -V O W g S 3 dpq 2- i5<t s3r s S O -t 3" S. 2 ? 3 O p <t g*I 5 tN>0fQ I S I 3 *D Si "<3t 2a . 2 1 ^ C e r " " - i f 2 . " 2 j 2 . 3* P* y 3 p n i = c r - <> jr . R w? 3 .if O r* 2 . 3* P 3 H CL O Z 3 g T it n 8 p ,=r s - ^ 3 3 ? 8 8 ^ 'g 5 2 12 . p 33 3 a i1 co V* s 3 2. 31 ST ? I o cco 3 S' 3 3 wp o S. __<t CO p(o w^ 3it* O3 *S-1i<a^ --. o 3 a3* nc>r n> -i . :p n 3> 3* 3 . co 0 O 3. co p 5 ?T 3a ^i3 n O o *3o 3* E--s I' UM P A L U t l A L.-- X U jU lL .^ u i . 1 j w - i . w ,., P rotective A ction of A lum inum Compounds When colloidal aluminum hydroxide had been added to a suspension of long fiber chrysotile prior to injecting this suspension intratracheally into rats, the aluminum compound did not prevent the irritation of tissue due to chrysotile. If anything, the acute inflammatory response evoked by the injected fibrous mineral was accelerated. One month after the last injection of the dust suspension the bronchiolitis was becoming fibrous. King and his associates also found that aluminum failed to protect pulmonary tissue from the irritation caused by asbestos fibers11; in their experiments metallic aluminum was used instead of the hydroxide. F ormation of A sbestosis Bodies The iron in the coating of the asbestosis body appears to be derived from blood or tissue elements and not, as has been suggested, from the mineral fiber. After two kinds of chrysotile were injected subcutaneously into the groin of a guinea pig--one kind containing 2 per cent and the other 0.2 per cent ferric oxide--the asbestosis bodies were equally numerous at both sites of injection and showed no difference in their reaction to prussian blue, the reagent which stains iron. This finding is in agreement with that of Giroux.1* T issue Reaction to A sbestosis Bodies Asbestosis bodies recovered from human lung tissue and injected intratracheally into guinea pigs failed to produce a fibrous reaction. The material for injection was obtained by digesting with sodium hypochlorite solution the lung tissue removed at autopsy from an asbestos worker. The asbestosis bodies could be seen in the guinea pigs for at least a year after injection. This experiment shows that the asbestosis body has a rather resistant coating which is not destroyed by moderate hypochlorite treatment, which may be maintained in vivo for a year or longer and which renders the fiber incapable of producing fibrosis. It thus appears that the coating is a protective mechanism. This thought was expressed by Beintker as early as 1934.1* THEORY OF IRRITANT ACTION Two hypotheses have been proposed to explain the tissue irritation and reaction caused by asbestos fibers : the chemical and the mechanical. In the chemical theory, which is based on experience with quartz, it is assumed that the asbestos minerals dissolve in the body fluids and that in this process their bases are leached away to leave silica in a form capable of irritating tissues. According to this hypothesis asbestosis is merely an indirect silicosis. Several facts make the chemical theory ! untenable: Intratracheal injection of hructte fibers, which had a silica 12. Giroux, M .: Amiantose exprimentale: valeur pathognomonique du "corps d'amiante," Laval md. 8:239, 1943. 13. Beintker, R : ber die Asbestosiskrperchen : Bemerkungen zu der Arbcit von Beger, Virchows Arch. f. path. Anat. 898:527, 1934. content of only 0.90 per cent, caused typical fibrosis like tliat produced by the asbestos minerals; free silica particles increase in potency as the particle size becomes less, but asbestos fibers shorter than about 10 to 20 microns are relatively innocuous; aluminum hydroxide neutralizes the irritating effect of quartz but not of asbestos; serpentine has the same chemical composition as long fiber chrysotile, but it produced only an inert type of tissue reaction; there is a wide range in the chemical composition of the minerals which do cause asbestosis (table 19). In view of this evidence it seems more likely that asbestosis is caused by an unusual mechanical irritation due to long asbestos fibers, this irritation being related to the peculiar filamented structure of the fiber and the associated flexibility, which are possessed by no other foreign body studied. Thus, ignition of chrysotile fibers changed their structure and made them inert, although the same fibers, before being heated, would have produced fibrosis (table 14). Further support for the theory of mechanical irritation is that asbestosis occurs in an organ of high mobility --the lung--and that a fibrous reaction can be produced by injecting T able 19.--Analyses of Fibrous Minerals Fibrous Minerals AmosIte........................ Amphibole.................... Anthoptiylllte............... Brncite........................ Chrysotile.................... Crocldollte.................... Treraollte...................... SiOs it 16.23 5.04 59.30 0.90 38.36 54.99 56.20 FcOj % 4.00 3.06 0.57 6.78 2.35 16.27 7.21 FeO AhOa CsO % % % 33.33 1.09 2.01 1.69 12.22 0.32 0.44 9.36 0.46 0.04 0.S4 0.03 4.29 LOI 0.80 0.56 4.44 MgO % 0.23 23.29 33.37 53.99 38.95 12.25 20.52 NeaO % 0.33 0.43 0.52 0.91 0.29 6.92 6.78 KtO % 0.20 0.12 0.15 0.16 0.06 0.57 0.99 Ignition L o n . < 195 C. > 105 O. %%% 0.66 5.28 0.32 3.60 0.27 4.08 0.53 26. 4 14.99 0.02 2 0.34 2.78 Total 99.97 99.77 99.52 99.7? 99.89 99.03 99.82< asbestos fibers into the peritoneum, where there is also a degree of mobility, but not by injecting them into other extrapulmonary organs such as the liver, the spleen and subcutaneous tissue. COMPLICATIONS The experimental investigations with asbestos minerals were con cerned primarily with the effect of the dust on normal tissue, but some attention was given to other phases, such as susceptibility to infection. The only experiment in which the effect of asbestos dust on a pulmonary infection was studied was the first inhalation experiment, carried on with King's floats dust. It is unfortunate that, owing to the lack of adequate facilities at that time, infection studies could not be made in the other inhalation experiments also. S usceptibility to T uberculous I nfection t The development of a tuberculous process initiated at the beginning of exposure to dust, and also of a tuberculous infection superimposed on an established asbestosis, was described in preceding sections of this paper. It may be stated that asbestos when classified according to the effect of a dust on tuberculous infection would be placed below an active dust like quartz but r infected with attenui process to progress i have no effect on tl. disease disappears, experimental investig ing the evolution of tl process for a time, bu the tubercle bacilli w: healing followed, T* bacilli after being ex years, progressive di the infection was one fibrous terminal bron the usual foci beneath S uscept There was no sp< asbestos dust on nont rather common amon in guinea pigs expose 16 to 39 per cent. 1 an effect of asbestos since such epidemics : other dusts and even inhalation of asbestos susceptibility to nontu Owing to the vast seems most convenient the various observatio follow each with a brii A. Various species of rabbit, but not tlfibrosis of the lun by inhalation or ii. fibers. Both inhalation an for this statement. Fi in guinea pigs followin the fibrosis caused in . Similar but less extet (table 1). Mice and d of different species to i B. Long asbestos fiber chiolar fibrosis; slv t VORWALD ET A L . S T U D I E S OF ASBESTOSIS 41 dust like quartz but above an inert dust such as iron oxide. In animals infected with attenuated tubercle bacilli, quartz causes the infectious process to progress until the animal dies of tuberculosis. Inert dusts have no effect on the infection, and the lesions usually heal and the disease disappears. Asbestos dust is in a different category. In the experimental investigation, when the fibrous dust was being inhaled dur ing the evolution of the infection, there was spreading of the tuberculous process for a time, but usually the stimulus for continued proliferation of the tubercle bacilli was not sustained, the progression was arrested and healing followed. In guinea pigs infected with attenuated tubercle bacilli after being exposed to asbestos dust for slightly more than two years, progressive disease did not develop. The only modification of the infection was one of localization, a few bacilli being retained in the fibrous terminal bronchioles and forming tubercles there, in addition to the usual foci beneath the pleura. Such tubercles healed in a few months. S usceptibility to N ontcberculous I nfection There was no specific experiment concerning the effect of inhaled asbestos dust on nontuberculous infection. Intercurrent pneumonia was rather common among animals exposed to asbestos dust, the frequency in guinea pigs exposed in the four inhalation experiments ranging from 16 to 39 per cent. This incidental evidence suggests the possibility of an effect of asbestos dust on nontuberculous infection. Nevertheless, since such epidemics are not uncommon in inhalation experiments with other dusts and even in the colony of normal animals, it is felt that the inhalation of asbestos dust does not exert a significant effect on the susceptibility to nontuberculous pulmonary infection. COMMENT AND SUMMARY Owing to the vast amount of data included in this investigation, it seems most convenient to summarize and to state as concisely as possible the various observations which emerged from the experiments and to follow each with a brief resume of the evidence. A. Various species of animals, including the guinea pig, the rat and the rabbit, but not the mouse and the dog, develop peribronchiolar fibrosis of the lung similar to human asbestosis after being exposed by inhalation or intratracheal injection to long chrysotile asbestos fibers. Both inhalation and injection experiments provide ample support for this statement. Figure 8 A reveals the cellular fibrosis that occurs in guinea pigs following inhalation of long fiber asbestos; figure 9 shows the fibrosis caused in the cat by inhalation of long fiber asbestos dust. Similar but less extensive fibrosis occurred also in rats and rabbits (table 1). Mice and dogs failed to respond. This variation in response of different species to identical dust exposures is still to be accounted for. B. Long asbestos fibers are essential in the production of the peribron chiolar fibrosis; short fibers are incapable of producing this reaction. 42 IN D U S T R IA L H Y G IE N E A N D O C C U PA TIO N AL M E D IC IN E Inhalation experiments with asbestos dust suggest, and intra tracheal injection experiments confirm, that peribronchiolar fibrosis is produced by asbestos fibers between 20 and 50 microns in length but not by particles shorter than 20 microns (tables 16 and 18). This indicates that the minimum length of fiber possessing the capacity to produce the typical peribronchiolar fibrosis in animals is somewhere between 20 and 50 microns. Pointed studies have not been carried out to determine the upper limit of effective fiber length. I t appears, however, that that limit will be determined by the inhalability of the fiber. C. The mode of action of the long asbestos fiber in the production of asbestosis is primarily mechanical rather than chemical in nature. The evidence for this conclusion has been reviewed in a preceding section, page 39. The flexible filamented structure of asbestos fibers plays an essential part in the irritating action, since the solid, inflexible fibers of glass wool do not produce fibrosis (fig. 13 B ) . D. Typical experimental asbestosis was produced by the inhalation of an atmospheric suspension containing an average of 138 million asbestos particles per cubic foot of air by light field count, of which less than 1 per cent consisted of fibers longer than 10 microns. In the inhalation experiment with 100 per cent ball-milled asbestos dust containing 0.6 per cent of fibers longer than 10 microns (table 11) typical fibrosis was obtained (table 9). The evidence presented shows at least that an atmospheric concentration of asbestos dust containing less than 1 million (0.6 per cent X 138 million) fibers longer than 10 microns p<-r cubic foot of air is capable of producing experimental asbestosis in guinea pigs. The actual lower limit of concentration of long fibers necessary to produce asbestosis in animals cannot be estab lished from these studies. E. The duration of exposure required to develop the pulmonary reaction to inhaled asbestos dust is inversely proportional to the concentration of long fibers in the atmosphere; as the concentration is increased, . the reaction develops in shorter time. The basis for this statement appears in the data of the inhalation experiment with long fiber asbestos. For that experiment the average concentration of the atmospheric dust was about 40 million particles per cubic foot of air, and size-frequency determinations disclosed that 6.7 per cent of the air-suspended material consisted of fibers longer than 10 microns (table 11). Thus, by calculation, it is estimated that the con centration of the longer fibers was 2.7 million (6.7 per cent X 40 mil lion). The lungs of animals exposed to the long fiber asbestos dust revealed that the pulmonary reaction developed in approximately onehalf the exposure time required for its development in animals inhaling the ball-milled product, for which the concentration of the longer fibers was only 0.8 million (0.6 per cent X 138 million). F. Established experimental asbestosis ceases to progress on discon tinuance of dust exposure. The experimental investigation shows, in fact, that on discontinuance of exposure there was an appreciable clearing of the mature nulmnnnrv VORW ALD ET lesions, due to contraction ture tissue response, evid fibrosis, continued to progof fibrotic maturity, the sa noted for the mature lesior G. The formation of asbe by blood and tissue ei fiber to produce fibro? Intratracheal injection typical asbestotic tissue re of progressive reaction ob due to the formation of as H. Aluminum hydroxide long fiber asbestos. Aluminum hydroxide prior to intratracheal injec of asbestosis in rats. I. Inhalation of asbestos <: of experimental tuberc the dust. The apparently mild i to the stimulating effect process in the lung. The since it is based on an in' exposed to only one kind shows that when the inf< exposure, there was tern with subsequent healing; dust exposure, the course The latter finding is quite dust or with mixed dusts c of quartz on a tuberculou infection is initiated after on a background of estah' sensitive test, when appli the latter had an advert inability of asbestos dust tuberculous process fum. inhaled asbestos dust has pulmonary tuberculosis. This investigation was ngroup of companies of the a VORWALD E T AL.--STUDIES OF ASBESTOSIS 43 lesions, due to contraction of the fibrous tissue. In contrast, an imma ture tissue response, evidenced primarily by cells with little or no fibrosis, continued to progress. It is assumed that, following attainment of fibrotic maturity, the same process of contraction would ensue as was noted for the mature lesion. G. The formation of asbestosis bodies represents a coating of the fibers by blood and tissue elements, which results in loss of ability of the fiber to produce fibrosis. Intratracheal injection of asbestosis bodies failed to produce the typical asbestotic tissue reaction in experimental animals. The cessation of progressive reaction observed soon after exposure terminates may be due to the formation of asbestosis bodies. H. Aluminum hydroxide failed to neutralize the fibrosing action of the long fiber asbestos. Aluminum hydroxide added to the suspension of chrysotile asbestos prior to intratracheal injection did not retard or prevent the development of asbestosis in rats. I. Inhalation of asbestos dust did not alter significantly the final outcome of experimental tuberculosis in two series of guinea pigs exposed to the dust. The apparently mild influence of asbestos dust is in distinct contrast to the stimulating effect exerted by inhaled quartz on a tuberculous process in the lung. The interpretation must remain tentative, however, since it is based on an investigation limited to two series of guinea pigs exposed to only one kind of asbestos, namely, King's floats: Table 4 shows that when the infection was coincidental with the onset of dust exposure, there was temporary progression of the infectious process, with subsequent healing; when infection was initiated after 26 months of dust exposure, the course of the tuberculosis was not appreciably altered. The latter finding is quite different from our usual experience with quartz dust or with mixed dusts containing quartz, wherein the adverse influence of quartz on a tuberculous infection is manifested most strikingly when infection is initiated after a period of dust exposure, viz., superimposed on a background of established silicosis. As indicated above, this more sensitive test, when applied to asbestos dust, failed to demonstrate that the latter had an adverse influence on a tuberculous infection. The inability of asbestos dust in that experiment to affect unfavorably the tuberculous process furnishes strong support for the interpretation that inhaled asbestos dust has no more than a mildly unfavorable effect on pulmonary tuberculosis. This investigation was made possible by the generous financial support of a group of companies of the asbestos industry.