Document 1g4Kp4QGBeroNZ14pn2qVGJRE

r-J *d I 1 /1 -v^ HARVARD UNWCTSfTV SCHOOL Of MEDICINE AND HWilUO HEALTH ESBJT :i. , ..UNITED STATES TREASURY DEPARTMENT j' --------------------------------------------------------------------------------------------------------------* " gj<r PSW PUBLIC HEALTH Iv- r , REPORTS ISSUED WEEKLY BY THE UNITED STATES PUBLIC HEALTH SERVICE Volume 53 Number 83 AUGUST 19...............1938 IN THIS ISSUE Endemic Fluorosis and Its Relation to Dental Caries - Medical Aspects of Silicosis and Preventive Measures Prevalence of Trichinosis and Measures for Control mjliml .... /r-JSfc A-irtfW tea , -yn\K rai lit f!&$F mi ri&. 7.1$. WS-OfeiL i.'l'.iVv: i *** ' . >1 ' ! ' $'' H' ! I UNITED STATES GOVERNMENT PRJNTINO OFFICE WASHINGTON 11038 i ^ oto Ay Ik* SuscriiitMdm el Daomett*, Wuhingtan, D. C. '-jjfer , Subtiflytion pno*.AS * yew n Prtot 6 aenu ( Vugoii i*. long 1452 Dakota, Colorado, and Wisconsin) indicates that the severity of dental caries is, in general, lower in molded enamel arena as com pared with normnl areas in the same State. 3. Inasmuch as it appears that the mineral composition of the drinking water may have an important bearing on the incidence of dental caries in a community, the possibility of p&rtinlly controlling dental caries through the domestic water mipply warrants thorough epidemiological-chemical study. y/ ' ACKKOWLKDGUXKT The outline of the artesian basin in eastern South Dakota shown in figure 1 was taken from plate LXIX, by N. H. Dorton, in part 2 of the Seventeenth Annual Report of the United States Geological Survey, 18U5-96. The writer desires to express his indebtedness to Senior Statistician Wm. M. Gufafer and Senior Chemist E. Elvove, National Institute of Health, for many helpful suggestions and criticisms in the prepara tion of this paper, to the Wisconsin State Board of Health for supplying information on the fluoride content of the water supplies of the seven Wisconsin cities with high dental caries attack rates, and to Principal Statistician Selwya D. Collins, National Institute of Health, for a review of the paper. - BETKttEMCKS U) Mack, G. V. (in collaboration with McKay, F. S.): Mottled teeth. An / endemic developmental imperfection of the teeth, heretofore unknown in the literature of dentistry. Dent. Cosmos, Et: 129-156 (February 1916). (A McKay. K. S. (in collaboration with Blurt, G. V.): An investigation of mottled teeth. Dent. Cosmos, 58: 477-181 (May 10(G). _ v (3) Masalii. T.: Geographic distribution of "mottled teeth1' In Japan. Sliikwa Cakuho. 86: (October 1931). . (4) Medical Research Counci], Special Report Series No. 07, II, The Incidence of Denial Disease in Children.' ills Majesty's Stationery Office, London, - 1925. , (5) Ain-worlU. N. J.: Mottled teeth. Brit. Dent. J., 55: 233-250 and 274-276 (September 1933). '' y (5) ErantHpiiii. R.: Dicnha veteadoa Rev. Odont. (Bueno* Aires), 23: 296-313 (May 1935). , (7) McKay, F. &: The establishment of n definite relation between enamel that is defective in its structure, ns mottled enamel, and the liahilily to decay, / II. Dent. Cosmos, 71: 747-755 (August 1929) (8) Dean, H. T., and Eivore, K.: Studies on the minimal threshold of tire dental sign of chronic endemic fluorosis (mottled enamel). Pub. Health Rep., 50: 1719-1729 (Dee. 6, 193a). (Reprint Mo. 1721.) 1/ (9) Dean, il. T., and Elvove, EX; Rome epidemiological aspects of chronic endemic dental fluorosis. Am. J. Pub. Health, 26: 567-575 (June 1936). v/ (JO) Dean, It. T-, and HHvoVo R: Further studies on tlie minimal tliresbobi of chronic endrniic dental fluorosis. Pub. Health Hep., 52: 1349-1281 (Fcpt. 10. 1937). (Reprint No. 1857.) J (IS) Dental survey of school children, agra 6-14 years, mailo iu 1933 -34 hi 26 Flaics. Public Health Bulletin No. 226. U- S. Public Health Service, Washington, 11. C., May 1936- v (J;) Bcs.cviiir>. C. H.: The presence of fluorine in the water su|M>ly of Colorarlo nl its relation to the occurrcnco oi mottled enamel. Colorado Med., SO: 142-1)8 (April. 1933). ( 1453 humianii SILICOSIS AND SIMILAR DUST DISEASES Medical Aspects and Control : By R- R. Saveos, ftirnr Surgeon, and R. R. Jones, Pmted Anutonf Srofeon, United Slate* Public Health Service . The pneumoconioses represent a class or type of diseases of the lung which develop slowly as a result of occupational exposure. The term "pneumoconiosis'* may be applied to any pathological condition of the lung produced by tbo inhalation of dust. It is common further to classify pneumoconiosis according to the chief constituents of the dust producing the condition; for example, silicosis produced by silica, ashestosia produced by asbestos, siderusis produced hy iron, antkracosis produced by carbon particles', etc. Of these, silicosis and osbestosis ore by far the most important from the viewpoint of number of workers exposed and the disability associated will) theirdevelopment. Since silicosis is the most important, end control measures effective in preventing silicosis are applicable in the prevention of other forma of pneumoconiosis, this discussion will be limited chiefly to reporting a summary of our knowledge concerning the cause and prevention of silicosis. The Committee on Pneumoconiosis of the Industrial Hygiene Sec tion of the American Public Health Association (i), defined silicosis os follows: A disease due to breathing air containing silica (SiO,), characterised anatomicnl)y by generalized fibrotic changes, and the development of miliary oodillation in both lungs, and clinically by shortness of breath, decreased cliesi aipuuion, lessened capacity for work, absence of fever, increased susceptibility to tubercu losis (some or all of which symptoms may bo present), and by characteristic X-ray findings. This definition of the disease seems to be satisfactory from a medical point of view; however, in a law recently passed iu West Virginia, for the purpose of the act silicosis was defined au an insidious fibrotic disease of the lung or lungs, due to prolonged inhalation and aceuinula- > tion, sustained in the course of and resulting from employment, of minute particles of dust containing silicon dioxide (SiO,) over such a period of time and in such amounts as result in the substitution of fibrous tissue for normal lung tissues; and the term silicosis shall also include silicosis accompanied by tuberculosis of the lungs evidenced by the presence of tubercle bacillus in the sputum. While the foregoing definitions of silicosis were obtained from sources that might bo expected to have somewhat different views, all have oue thing in common--that the cause is silica or quartz. Although other dusts, when inluded in sufficient concentrations over & long period of time, have been shown to be capable of producing a jlfifiiiit4> milmnnuMr --------------IV .1.- . a* - - .. , ( Aasjori Itt, tttt 1454 acterized by nodular fibrosis has to data been shown clinically and experiment idly to be associated only with the inhalation of dusts containing silica. According to Dorland's Medical Dictionary, "Pneumoconiosis is a lung disease due to the inhalation of minute particles of dust. It in attended hy fibroid induration." Pneumoconiosis is a general term, and tho lung disease caused by any one dust usually takes the name of that dust, as anthrocqsis, silicosis, chalicasis, siderosis, and asbestosis. ' SILICA IN NATUHE Silica is the most abundant constituent of the minerals and rocks that make up the crust of the earth. It occurs in two forms, free and combined. The free silicas as a group are definite compounds in the form of SiOj. The combined forms are silicates. Of free silicas which occur in nature, that known as quartz is by for the most common. Quartz is hard mineral and chemically resistant to reagents. It is an abundant constituent of granite, schist, and other rocks, ond the chief component of sandstone and quartzite. Many ores are deposited in veins that consist nearly wholly of quartz. Probably the next most common form in which free silica exists in nature is the amorphous hydrated form known as opaTfSiOj-IIjD). Opal is a tilica of colloidal origin and occurs abundantly in the diatomaceous earths. It is less resistant to reagents than quartz. Another type of free silica fre quently found is flint; and with flint is found chalcedony, a waxy, translucent form of silica interpreted as consisting of fibers of quartz with a small amount of interstitial opal. Other forma of free silica occurring less abundantly in nature are tridymite, cristebnlite, and siliceous glass, or vitreous silica. " OCCUPATIONAt KXFOSUUK TO SILICA . Owing to the fact that the earth's crust contains so great an amount of silica, it is obvious that those occupations concerned with the driving of tunnels, development of highways, and mining are fre quently associated with a silicosis hazard. A second class of occupa tions exposing the workers to this hazard ore those connected with industries that have to do with the processing and industrial use of mineral products, such as the smelting and refining of ores, the use of sand and gravel for structural purposes, the carving of stone, particu larly granite, the manufacture and use of certain abrasives, nod the processing of the various forms of free silica. According to Knopf (), the most common forms of free silica used industrially are massive crystalline quartz, quartzite, sandstone, flint, tripoli, diatomaceous earths, anil silica sand. Table 1, from Ladoo (9), illustrates the great variety of uses to which silica is put in industry and shows the kind of silica ncktnUvl lev cneh nnran^ (( 1455 Auflugt i. urn Table 1.-- (7tn / ait/ca ttasorflOica Types erf silica used Abraart use*: la scouring and paHahteg soaja and powdra*. __ Quarts, qoartrite, iint. chat, apdfinn, ncd. Iripdi sad diibnmoMawitli; all ta In4y gnnd *tau. la nodpaper............. .............. .......................... Qonti, QUaiLziU, flint, aotblflM, and nud; erantly ground sod riotaiy rirod- la saad-toftast wrli_.________________ Qflata, qnartzir*. fttuetMwm, and aand.emshtd into sharp fgghjw pralne uniform la rtfy Metal buffing: kocn&itig. and pointing -....... Oram) bdpoll and other bnutfpmiildlk*. Fur rawing and pnlisbio* jwartde. penile, etc.. Sfcacpk eleeo sand graded Inin varum decs. As <rhalftone, grindstoara, fcuhcstoiiM. poll*- Massive nsdstocra tnnu eery Sen ta swderaufty MwtSiflikbmdfl cmnecraoed- Tnte~jsi& lining___________ ___ ____________ Ourt.Sul. and qralzQe to dense. Mid blocks. LUtographia' graining sand------ ------- ------ -- Medina to flneannd cr rather enndr ppunddika and triprii. Tube-mDI grind)uc pebbles_______ __________ Rmmded dial pebblen. In tooth powders ami petite*---------- ....--------- Vtfkw forms at parr liln luei; ground. Wend end <inhhf__________ _ AG Come d often pvuid to joedim Irrarra ' pdndkit isu; keutiofliliisbiUidiadfiUief Flirty pun juartte hnawu aa poulte; not leas efiHitcBtan. than Iff Most &iO Mr awe than Id prowt nlkaloM, lightly ahviockingpumtebd. bintslhenfcnl uses: In rnnKEngjiliciii, fentdlkotL and sflaxmalloy* Moderately pore rand, mash* ovildUne quarto. d dfau mttak. such is cupper. suhtMi turtiii* cr ehaxL Aiaflas msnulttag baste era*..-..................... Moratra quart* and guarbit#. Foundry-mold vnb. ------------------ ------- Gnnitti awWue, quart*. and IrIfaiB. Foundry parting rami.__ __________..._______ Finn sand and ground tripoli. Chunked judiuiries: A* a Items far arid Umars---------------------------As * Altering Hkodimn-............--...--------- ... Massive quarts v qumtiite. Maadro dialouacecme earth and trlpotlnad. OkIt Sreader qmrU at quatdin. flnety ground tripouL toflwitran rartly and other hams rtallm. In tba manufM.im of sndiuin aelicate. --....... Fora pelvcjriiedtMUaaaM]. pore fripofl,end dtalomarautu earth. In tbaraoonlMiaroof carborraadara---------- -- Faint: As au inertcetandar--------- ------ ----- Fura quart* iaad. Finely(veaadcryetolVnaqaafta. quastyhe, sudflel; aba Andy poundranrirtortf, sand,end tiipofc. Mineral JDIetft: Ae n wood fllhr-...___________ Finely proud errdalUaa quarts, opablle, (Hot, tripci, and other typos at ground iuU. In bliliier--........................ ......... --.........-- la taarlicidra--........ .............................................. A* a Alkr la rubber, bard robber pressed and Finely ground silica erf all types. molded poods, phonograph records, ale. Inroad asphalt wafactog alitues------- -------- Ctruolcws: la the pedlary industry as ao inps- flint, trfpoh. and chert* and other eraarphoes aOfra pratoed; aba aD ether bania id racy praa sdka. aB Anail1 ground. lotbonufMUraiiiioof radtaaryglara------------------- Fora quarlr sand, Inltvamosnilaotura orffinod^inarts duoituspiuk Vecy pare auriw quarto juieiei ralnesBCb astobus. oudfala, end dishe*. DeardlniiuMtfab: In the nMwhdan oC gun*. Rack crystal, amethyst* rose quits, dlrtae qeartc, <*y**l bale, tabletop* van, rtstne*. etc. snaky quarts, duyuprasa qalq fhdtetoi, oprii any*. eardoayr, Jaapra, ate. IrafdiMi: Heat inalathn ter pipe* hofien, furnaces, Mnaim usd ground dialamaccrue earth. SoUunud,laetach. Uan la walx, Irtdwm flOOD), Cte... Do. dlractoralaraHrishi teuHtia brick--............ Mmlaatdypao,rittrc,anruImrttad,praferaMy flora than Rank, toyetber with auuufl perceoiape of Auely odverkad allien. Optical quilr For tha rasoiiheluc ritocs cod Clear, eiwlra,tewtonek njtel cr nisdnap- aceerafaiea for opIicM eppraetiMw taMeed quart* ' Id a recent survey (j) carried on in a large manufacturing center, it was found that about 9 percent of tha industrial workers were employed in occupations where the silica hazard required consider ation. According to the census for 1930, there were gainfully em ployed in the manufacturing ond mechanical industries in this country approximately 14 million persons. If the above mentioned survey can be accepted as representative of the occupational distri bution oC these workers, it appears that there are nearly 1,200,000 1* ; i ,i. ...i. .if ii * * v ' * i I IC i( I r i ? i ! *4 i I ( August UL ISM 1456 taring and mechanical industries alouc. Lanza and Vane (J), in their discussion concerning the prevalence and effect of silicosis, state: "Our very rough, but obviously conservative, estimate of the number of workers exposed to silica dust to a harmful degree in (he United States is, therefore, upwards of 500,000." FA CTO03 INFLUENCING THE ACTION OF SILICA DUST PAKTICLES AS THE 8^CITING CAUSE OF SILICOSIS Although it has been accepted that silica is the exciting cause of silicosis, there are certain factors which must be considered as influ encing its action. Tissue reaction to dud.--Early workers were inclined to consider that the injury caused by the dost particle was due to mechanical irritation produced by its hard aud cutting edges. Gardner (6) has shown experimentally that the inhalation of finely divided carbo rundum dust having sharp edges, of a greater hardness than silica particles, does not produce the nodular reaction characteristic of silicosis. Collis (7) was one of the early workers to draw our attention to the chemical action of dust. Gye and Kettle (6) have shown that silica in solution or nancrystalline form exerts a toxic action upon the tissues which leads to the proliferation of fibroblastic cells. Lately, Miller and Sayers (3) have reported results of experimental studies which illustrate dearly the reaction of peritoneal tissues to certain dusts. Only the silica-containing dusts have uniformly produced a proliferative reaction. Other dusts have been either completely absorbed, leaving no sear tissue, or have remained unaltered in the farm in which they were injected. These latter reactions axe dossed as "absorptive" or "inart." Size oj dust particles.--Since dust, to exert its harmful action, must enter the finer divisions of the lung, the particle size of the atmos pheric dust bears a definite relationship to the injurious effect pro duced. The silica must be present in the air in particles small enough to enter the finer air spaces and of such dimensions that the phagocytic cells may engulf them. The natural defenses of the respiratory tract probably prevent many particles larger than 10 microns from ever reaching the finer divisions of the lung, and such as do ore likely to bo expelled with the bronchial secretions. Thesolublesilica plays a definite part in the production of the disease, and the size of the particle also affects the rate of solution, due to the fact that the smaller the particles the greater the total surface area exposed to the action of solvents. Table 2 shows the ewe distribution of various industrial dusts as compared with the dust partides observed iu the outdoor air in the general atmosphere. Apparently about 70 percent of the partides found in industrial dusts generally are between 0.5 and 3 microns iu T asle 2.-- Siie~frequtncy a ttrib u tio n of variou industrial dustt a t compand to outdoor d u tt1 [Atoms Irtoutdty fa fwoent) s i o i s i * > i r3ii Iaa3 2 2 &4 o rt IS as w ca d. s 2 t4 <a *7 s t o 3 i I it H 1 O I~ 1457 n i i O <009 a k t > t 1 ti i i11!:;; | i:::hj!;it 1114 : lilt: a a c*o 64 a o a * lIS!! * 1 a a a * *t a a i j?00?9 a sl a a i 5: :: >44# nn SiS! O iO0 a ilia* d' ISS! Iririd a XE i a 4 ! i Hill S S !a 000< a * s s eiHHidn a a a* a a a2 i: :::: a i aa 1 i<6ae !:wd iji S>44 * no >0 | jd OO a : 9 a t ! a am 1! S 4 i a : s:: : e ! a>* oou NIC tidrirS 0d4 c(4 ' * * n loiooaoaoooee oo w4idd4 ! '4 -------- j noonooGccoo eo^< 66 c: o vd efi *r O ^4 N OOOa^aOOOOO 004I&A "**s risxsa">r-w OoOe^oooooa* das dsass01*0 OJO0OO 0 0 9000 OOOM0 0<*0 00* a So Setoo 00000 |4 |r*ei4 1^4444 Ow WfQWMA>4aMi4 oaovo d H 4 r< *1 rf ri d 4 111 iliiiijiii! iiiii ft: it ii;: |:: 11 JjjilliisNsfil li ;|JI f!i|llaiii!!il|ils33i ( Auga* n. nm ( iutusi u. ins 1458 diameter. Thera .ora no doubt many limes as many particles too un&ll to count by the method used, but experimentally it has been shown that a great percentage of such Gubmicrracopii*, particles are not retained in the lungs bat pass out with the expired air. Sayers 00) has shown that less than 15 percent is retained when the finer particulate matter, such as lead in the form of fumes, is inhaled. The greater majority of particles found upon microscopic .examination of the lung also fail within the limits of from 1 to 3 microns. Another reason for considering the size of the particles es affecting the lumnfulness of Ute dust, is that it is the larger ones that settle out rapidly while the rate of failing for the smaller particles is very slow. Figure 1 illustrates graphically this difference; those under 1 micron faff at a rate of from 1 to 3 feet per hour, varying with the specific gravity, w hile u particle 5 microns in diameter of 7 specific gravity falls about 60 feet per hour. Particles of more than 10 microns would settle out in a relatively short time. The fact that the finer particles remain suspended in the atmosphere for long periods greatly increases their chance of being inhaled. Thus we may say, from (lie viewpoint of etiology, that the harmful ness of a given dust containing free silica is directly influenced by tire uumber of particles of free silica it contains less than 10 microns in diameter, and probably the greatest harm is produced by those between 1 and 3 microns. , ( 1459 Xgurtmm Coneentration oj dust in the atmosphere.--The relationship of dust concentration and duration of exposure are closely associated ia their etiological significance. The rate at which silicosis will develop, excluding certain factors considered as predisposing, depends upon the dosage of free silica. This dosage is obviously dependent upon the amount of silica in the air inhaled and the duration of exposure. In 1902, a committee, of which Dr. i. S. Haldane was a member, reported (if) upon on investigation mode to determine the cause of excessive mortality rates from tuberculosis among the Cornish tin miners. This group decided that it was evident that the inhalation of stone dust by these men in the performance of their tasks os miners was (he cause oi permanent damage produced upon the lungs. Furthermore, they noted that the condition developed gradually in the ease of the ordinary miner, but rapidly in the cose of the machine workers who were exposed to greater amounts of dust. Dr. WatkiraPitchford (fi) and Dr. Mavrogord&to (/$) and other South African workers, in their discussions relating to the etiology of silicosis, em phasize the relationship of the concentration of dust and duration of exposure to the degree of lung changes produced. M&vrogordato has suggested the advisability of intermittent employment os an aid in lessening the amount of changes produced; but aside from the fact that it does delay the reaction, it has not been shown that it coaid safely be relied on to prevent silicosis where exposure is to sufficient concentrations. Workers in tliis country have also shown the rela tionship of dosage to the severity of the reaction. Reports of the Picher Clinic (14), of the Tri-State District of Oklahoma, Kansas, and Missouri lead and zinc mines, which ia a cooperative undertaking, by agents of the operators, the Metropolitan life Insurance Co., the Bureau of Mines, and the Public Health Service have shown clearly the effects of various periods of exposure to silica as met with in the mining processes carried out in the district. Similar studies upon the health of granite workers (15) (iff) likewise stress the duration of exposure necessary to produce definite d^jroes of silicosis. Role played by other dusit present with ico.--Must authorities agree that the presence of other inorganic dusts in the silica-containing atmosphere may tend to influence the rate of progressive reaction resulting from inhaled silica. Some of them tend to alter somewhat the radiographic appearance so that the uodular shadows ore less discrete. Some have thought that the relative absence of silicosis in the cement industry was due to the euleium present. However, investiga tions (/7) have led to the belief that the absence of evidence of exten sive pulmonary fibrosis among employees in the cement industry is due to the /act that there is insufficient total exposure to free silica (con sidering the percent of free silica in tbo dust, concentration of dust, and ^ II ro I in n r>f n r*wi \ < 1400 Ko complete reports of pulmonary fibrosis resulting from the inhalation of organic dusts have appeared in the literature. Always when such fibrosis is associated with the breathing of air containing organic dust, either inorganic dust bus been shown to be present or at least its absence has not been definitely proved!. In regard to the presence of other irritating dusts. Chapman (18), Kessler (/*)), MacDonald (0), Kilgore (iff), and others have reported coses of so-called acute silicosis resulting from the inhalation of air containing high concentrations of silica along with strong alkali in a fine powdered form. Some have suggested that ilte rapid action of the silica in the production of pulmonary fibrosis is aided by the presence of these alkalis, because silica is more soluble in nHrnliTM solutions. Kettle (21) failed to demonstrate such actions asperimentolly and states that proof is stdi lacking that any action of tbs kind may occur. Pathological reports furnish evidence of a definite fibrosis; Jut the entire picture differs remarkably from that of the typical silicotic, such as has been furnished by Gardner (28) in Kin reports upon Uis examination of tissues from clinical cases of silicosis as well as his pathological reports made from tissues obtained in his experimental studies. Sayers, Meriwether, ruidi<anza (f^i reported that of the employees in the lead and sine mines, those who gave a history of previous coal mining experience developed a definite silicosis in a shorter time than ^employees of the some age without this experience. This cannot be taken to mean, however, that the inhalation of coal dust hastened the action of silica, fur it is doubtful wlietiter any of these coni miners hod worked where they were not exposed to some free silica, so that the total dosage of silica was not the some in the two groups. OCCOTAIIONAL HISTOUT An important factor in determining etiological significance of total dust expusure is a complete, carefully taken occupational history. Dftlcd: Aapudl, BH, MAgaeaut; CowwovfMc:kIr&fu. ai. Table 3.--Occupational record Offitt: Indotftriol Hygfeco. KFfutsaabiteocrfKlff4M0. aBKM: W- Bpocllki auiHVUfiA Minabcr d nui ni-- . Specific IfttluATj Banl real Non* hckfX: Sectioa fomaao_______________ _________ Aailwauiu ojfli.___ _ . hwetUni (xmetd: 1. Caoinrl miwt fctenbvr).............................. 2. Mnttn1 lnlmrrfrliuibcr). .... ................... . . .do... . . A AluktlrivcrlAyvuM)....... .. ___ ...................................... 4. FhSftei (tlry miu*).......................____ ____ _ .......to.................................. A pinktr (thy lawhn), ______ ... ___ to......____ ___ ...___ (1 Vfia Aiboviirthu). ... .............. ............. l u 3-- 1 2 2 ~- JtciiwriA. Ealirampfi teUI lim Mta riming warfcLftK life-1 ytuca. Uy recently (he eouipfcEo date. 8m tutnl ihari oiikNtim nwv In* ~.A ..... .... h ........ r - . ( 1461 AuetM,NH Table 3a shows the activities and associated dust exposures of chamber miners and laborers. It will be seen that each activity engaged in by those cool miners was studied separately. Experience has shown that the various occupations comprising the process of say dusty occupation ore usually associated with dissimilar dust exposure. Tnu ti.--Dtnl exposure of contract ttiMn sad helpers {loiterers--Qamtcr wining *01015 Number Unmilw Ntunbei dkmnfo irttvity Avexofc duiteooA niUltittd paiMto purubic autofair MHUoaMT falidtboaisper euMefct* hdHamiH dkiUiuCJlwt lOcUllBg_____ ..................................... ______ ________ 2n5 i 2 m 1.J3A ACtrr firing_______ -------------- -- ------------TapUif and wtriaf..................------- ------------------fetUbg up pcoi*, ud io main airway*. ____ _-- i2 A k H rii m * W Ul 14 n 41 TUH-.................... ........ M am mfliinn psitkMMhi per wbic foot equate (B miOin* naitfrfi-- |Kr cable ted tunm. It is apparent from this analysis that the hand loading of coal contributes about 73 percent of the total dust exposure of chamber miners and laborers, although tlus occupation comprises less than one-third of the total working hours. Jack-hammer drilling, which occupied but 1 hour of the 6H-hour iniaeni' day, amounts to 18 per cent of the total exposure, while the practice of entering a room too soon after blasting unduly exposes miners to a large amount of dust, this quantity being about 7 percent of the total dust exposure. Table 4 shows the method of analysis used to determine an estimate of the individual's total dust exposure. Tabu 1.--Estimation of lh utdiriduot* total dust exposure OecqiillU SOI* (ickcn (drr wie>-------------- --------- ----------hlctm (ilrV nua)--------------------------.............. Mall Slim (dq miar)------------------------ -----------14inert laborer (duitnl_________________ ____ C8koUUwltfttnmoinMeri_(c_h_am_b_e_r)_______________--___ .._.._..._.._..._... Total--------- ---------------------------------- -------lalBara o jartldr yriua (R. mb* It.,^ KunbcrfiC )rcot$ Dust caaeeatiathai iaatl- Kaaaof per- * ndapr ruble feat (tweet) aaiuau partieS-ycacs per casta Sot 2 2 3 3n8n0 A 480 U Ai XI ------ -------------- 7e Ut 211 1.M* T.m u XIW ^ Jtar3 floUe Morq detailed application of our knowledge of the true cause of silicosis'Is illustrated iu table 5. In this study of the actual duties required <by the job, it is revealed that the greatest hazard, so far as molflinff miiTBlinnfl r* wiiiwrnail in lt.nl " *l- ,h" "" ( AuvoM >- OM 1462 of a parting compound. It is generally agreed that tho moat impor tant silica exposure of moldera ia due to other silica-genemting proc esses often conducted in the vicinity of molding operations. It is obvious that the risk associated with molding operations can be materially lessened either by using a parting compound containing less silica or in properly safeguarding the user by adequate dust control during this operation. With such occupational histories avail able, and (ha knowledge pf the percentage of total dust exposure revealed by detailed occupational analysis, it was found possible in a recent study to prpphesy in 9 easesout of 10 approximately the condi tions that would be found upon physical examination in cases where tho total changes were due chiefly to dust inhalation. Table 5.--Dual nature of moltUrs Actiittr Tiniest Ofiaaaic inninntes W Avrnteduat npmotPiDUflItasal runties per cubic foot * MalicEH ol wticteminute* CttXb) U*t of portingtioittiMtvMl............. .............. __ ___Dfnmlshig till in nnUu* ______ nusirlilf tuofcfc OlniAft buO.............. Tool________ __ __ . --------------- -- _ M 412 SB Ik ft. 8 4.4 3.1 333 3,444 1,813 uc 4M* ttj0u& uttiw vartittaaiiniite* 448" U ioOUdi pnrtk&s per cflfaie foot. ^ PREDISPOSING CAUSES Geographical distribution.--Eight countries were represented at the International Conference held in Johannesburg in 1930. A recent bibliography on pneumoconiosis lists references to the literature of 26 countries. Since the literature of practically all the principal nations of the world contains articles on this subject, it is apparent that no national ity is exempt, and that aU races are susceptible is shown by the wide distribution of silicosis. Age.--Although the data show incidence is higher among the younger miners in districts where the percentage of free silica is high, and among older miners where tho percentage of silica is low, age in itself probably is no great factor.. Precious exposure.--Previous occupations of the men ore reported to have a definite influence in predisposing to silicosis, if they have been exposed to dust or to other respiratory irritants. Imliridval susceptibility.--The factor of individual susceptibility is often mentioned. Generally speaking, if there be any difference in individual susceptibility, it con usually be considered an acquired and uofc a congenital condition. Ickert (2{) quotes Bohme and Lucanus ( 1463 Angus a use and Schulte-Tigge aa staring that it is essential that the individual possess excellent functioning nasal passageways, in order that tire self cleansing mechanism may work efficiently, lie calls attention to the fact that Irvine, Sird^hon, and StrochaS^report the "classical" type of silicosis to be more common among the robust type of individuals with less respiratory reserve. Ickert found some slight variation in the susceptibility of persona according to their type of body build. As a whole, the group classed as slender individuals developed simple silicosis somewhat slower than the stonily built persons; but the Incidence of advanced silicosis was greater in the former doss, being nearly double that developing in tire sturdy workers. Lehniaun'a (25) experiments to determine the functional efficiency of the upper respiratory tract in the removal of dust, suggests that abnormalities of the nasal passageways probably play some part in the rapidity with which silicosis may develop. It is suggested by some that chronic bronchial asthma may be con sidered a predisposing factor affecting individual susceptibility. The spasmodic attacks, if frequent, lead tit a reduction ia the individual's vital capacity. Aside from the pulmonary fibream, other pathological manifestations of silicosis such as bronchiectasis, emphysema, and right heart hypertrophy and dilatation, may bo aggravated by this chronic condition. Hale of infection.--Since respiratory infection has been shown to be the greatest complicating factor in the development of silicosis, cer tainly the history of present and past respiratory infections will have to be given consideration in the statistical analysis of records upon which such conclusions are based. Infections developing along the respiratory tract may be of im portance. Sinus infections may act by decreasing tire efficiency of the upper respiratory tract in the removal of dust from the air passing to the lungs, and also they may be the source of infections that spread to the lower respiratory tract. Acute pneumonic conditions os well ns the more chronic lung changes such as chronic bronchitis, bronchi- petasis and bronchiolectasis, emphysema, and pleurisy, all tend to decrease the ability of the lung to rid itself of foreign materials, through lessened lymphatic drainage and decreased power to force the bronchial secretions and foreign matter from the lungs. Clinical fouling# and diagnosis.--The subjective and objective signs of silicosis vary according to the rate of development and degree of pulmonary fibrosis and, when infection is present, according to the type, extent, and duration of tlie complicating pulmonary infection. Early_in the course of the disease, signs of the condition may be absent dr slight, except for the changes revealed by X-ray examination. When suffieientfy developed, the most coaunun subjective signs are abortnesa nf Krooili ----1 -- 1' ( Aufdat W* IW8 1464 depending upon degree of development, the chief objective signs are shortness of breath, cough, prolonged expiration, decreased cheat expansion, altered breast sounds and rules, impaired resonance, and characteristic radiographic appearance of the lung fields. Diagnosis is based upon historical data, including the complete occupational history, past and present medical history, clinical, labora tory, and X-ray findings. Except by autopsy, silicosis cannot be diagnosed definitely until examination of the X-ray film reveals characteristic nodular shadows throughout both lung fields. A com plete diagnosis shobld include, in addition to the decision that silicosis is present, a statement as to whether or not there is evidence of a com plicating pulmonary infection; the type of infection if possible, and its extent; and, finally, a statement as to whether or not the individual manifests any decreased capacity for doing his usual work and an estimate as to the degree of Ids disability. Individuals with silicosis and active pulmonary tuberculosis are considered seriously disabled, and for the safety of themselves and others they should be barred per manently from work affording further exposure to a silica-bearing atmosphere, regardless of the manner in which the tuberculous infec tion may respond to treatment am] rest. As indicative of the affected individual's status under compensation laws, it has been customary to defuse the disease arbitrarily into stages--first, second, and third (/>. From a medical paint of view, there is no such dear line of demarcation. " First stage.--Chest film indicates early nodular fibrosis, the indi vidual may or may not exhibit such clinical evidence as slight short ness of breath upon exertion, and some cough. The general appear ance is that ofa healthy individual, and there is no appreciable decrease in capacity to perform usual duties. - Second stage.--More advanced nodillation is shown by X-ray, and there may be some evidence of localized aggregation of nodules and pleural thickening. Definite shortness of breath upon exertion, cough more pronounced, chest movements dsggish, and expansion usually decreased. The individual may be able to continue at bis usual job, although less effectively. Third stage.--Fibrous changes os shown by X-ray film are further accentuated. Nodules era larger and assume conglomerate form, showing huge shadows corresponding to areas of dense fibrosis. Short ness of breath is marked and distressing upon slight exertion. Cough is increased,and may be dry, but is usually productive. Chest expansion is decreased even upon forced inspiration. The individual's capacity fur work is seriously and permanently impaired. The stages just discussed would seem to indicate in a way the extent of disability or potential disability. However, those interested in silicosis are tending timrant the opinion that it ia beet to make a ( 1405 iiwiiain) decision as to whether the individual has silicosis or not, and to determine the extent of disability, if any, due to the disease, without reference to stage. TUBKBCULQSI3 AND B1LICOSI0 In 190S the Miners' Phthisis Committee of Australis, reported that gold miners there who contracted silicosis died of tuberculosis (98). The Increased incidence of tuberculosis among occupational groups exposed to silica has been dearly shown in every instance where this hoxard exists. Britten (97) summarised the report el the Bcgistrar- General of England and Wales for 1921-23, and showed the occupa tional mortality rate for the group of trades dossed as "Dusty Trades" to he from 3 to more than 10 times as high as the rate for all occupied and retired males. ,, . Tablb &--Slmuliintiaiil Tuorlahly from rfiratarp tuiercnluu in occupation* mil rates afawe average, welts age itO-65, fiifM and IKabs, UtSI SS . Duma and Vane (5) show by an analysis of the mortality experience of 12 life-insurance companies, for the period of 1915 to 1926, that the actual mortality from respiratory tuberculosis among tiw silicaexposed persons was about three times that of a non-silica-exposed group. When this comparison is limited to the rates for some of the occupations with a very great silica exposure, such os metal mining, sandstone, and granite quarries, the excess is still more striking, the rate being about 10 times that obtained in the non-silica-exposed ,, group. Gardner ($8) has shown that animala exposed to silica when inoc ulated with a strain of tubercle bacilli of low virulence will develop systemic tuberculosis and die, while control animals not so exposed usually ore not seriously affected by injections of such organisms. PIlOCBE&SiVB TENDENCY OF TH2 DISEASE Since infection has been shown to play an important role in the advanced seriousness of silicosis, the possible relationship of this infective dement to the progressive tendency of the disease cannot be overlqqjted. ;' Irvine (9) Has stated thst it is not no much what rt> wm^itinn of ( Augvl lSlM 1466 emphasizes the tendency of the fibrosis to progress, even though removed from exposure, and expresses his opinion that it is one of the most serious aspects of the whole silicosis problem. No remedy lias been shown to be of vulue in the elimination of the pulmonary fibrosis although improvement in symptoms may be noted after the victim ie r^ov<*l_J[rfiin exposure. According to the observations made by Bohmey^ochnm^ (30), silicosis progressed, after removal from expeatire, in 20 percent of the cases diagnosed as having silicosis in grade 1, in 40 percent of the cases in grade 2, and in practically all eases in grade 3. \ ; smen or othbb dusts It scorns to be the consensus of opinion that silica dust Is the most harmful, and it is the principal one with wiiich industry is concerned. However, asbestos is weported to be the one which produces a condi tion which is disabling and causes death. Ashestosis is relatively a new disease in industrial workers, os asbestos has not been in general use for so many years. Asbestos is an anhydrous form of magnesium silicate. The symptoms of asbestoaia are insidious in onset and irregular in the course of the disease. Dyspnea and cough are the most prominent, and as the disease pro gresses the cough becomes"productive. Elastic fibers can be found in the sputum in advanced cases, indicating that there is destruction of the pulmonary tissue. Asbestos bodies have been found in the sputum and the finding of them is & diagnostic aid, showing that the worker has been exposed to the dust. These particles of asbestos in the sputum usually show evidence of disintegration. Asbcstosia usually develops after exposure to the dust (excessive quantities) for a period of approximately 7 to 11 years (31). It has not been shown that osbcBtosis predisposes to tuberculosis as does silicosis. Death usually results from pneumonia, bronchitis, or influenza and less often from tuberculosis. When tuberculosis complicates osbestosis, the clinical picture is not the fulminating type. ' The X-ray characteristics of the chests of asbestos workers differ __ from those of workers exposed to silica dust. The markings are less distinct and are described by some ns having a "ground-glass appear ance." The nodular fibrosis of silicosis is conspicuously absent. Another form of pneumoconiosis occurs incident to exposure to magnesium silicate dust in the form of talc. This dust is a hydrous form of magnesium silicate, HiMg,(SiOj), and is used in a number of industrial processes. The mining and milling of talc entails exposure to excessive amounts of the dust. Dreessen (32) reports tbe results of a study of exposure to talc dust. He states that a fine bilateral fibrosis of the lunge occurs, which is demonstrable by the X-ray; and that while very dusty conditions prevail in the production of talc, it cannot he said that the resultant pneumoconiosis Iik led dw|iilifn ( 1467 Xufnt Bl 1KM A NTHHACO-BHJCOSI3 Antliraco-silicosis is the term used to describe a certain farm of pneumoconiosis, commonly called miners* asthma. It is a chronic condition due to breatiiing dust iucident to coal mining. It is char acterized by general fibrolic changes of tho lungs with the presence of excessive amounts of carbonaceous and siliceous materials. A com pensatory emphysema occurs and often cardiac changes take place in the later stages. The cool mining employees were grouped occupationally, largely in accordance with the proportion of free silica found in the dust to which they were exposed. - No cases of anthroeo-silieasis were found in a control group com posed of hard-coal mining employees whose dust exposure averaged less than 5 million particles per cubic loot of air. Tbe prevalence of anthraco-silicosis among the entire group of em ployees was found to be about 23 percent. Among men exposed 15 to 24 years to dust containing less than 5 percent free silica, 14 percent of those who had worked where the average dust count was 100 million to 190 million particles per cubic foot, 29 percent of those exposed to 200 million to 299 million particles, and 58 percent of the men who had worked for this period in more than 300 million particles per cubic foot, developed antbraco-silieosia. Among the men employed for more than 25 years in dust containing less than 5 percent free silica, the proportion of persons found with anthr&co-silicasis under different concentrations of dust was as follows: 5 million to 99 million particles, 7 percent; 100 million to 199 million particles, 54 percent; 200 million to 299 million particles, 71 percent; 300 million or more particles per cubic foot, 89 percent. With the exception of miners, their helpers, and rock workers, about 25 percent of all the men employed underground developed aathraco- silicusts after a working period of more than 25 years. This group was exposed to dust having a quartz content of about 13 percent. The prevalence of aulbraco-silicosis among persons who had been exposed for more than 2 or 3 years to dust of which about 35 percent was free silica, varied from 10 percent among those who had worked in concentrations of less than 200 million particles per cubic foot for less than 15 years, to 92 percent among those who had been employed for more tlum 25 years in dust concentrations exceeding 300 million particles per cubic foot, more than 2 or 3 yearn of which time was spent in rock work. . Age per at appeared to play only a minor role in the development of xnthraco-silicoKjg. Analysis of the data for the purpose of determining safe limits of (lll&t #*Ynnanr*tt ---- ----- 1 * 1* ' ( Aaguit Hi HU 14G8 taming less than 50 million dust particles per cubic foot would pro duce a negligible number of case? of unthruco-silicosis when the quarts content of the dust was less than 5 percent. In the gangways where the silica content of the dust was about 13 percent, a safe limit appeared to be 10 million to 15 million particles per cubic foot. The limit of toleration for rock workers was set tentatively at 5 million to 10 million particles per cubic foot of air. Pulmonary infection increased with length of service more rapidly among tho men in the haulageways than in the control group, and much more rapidly' among the regular miners. The highest rates of pulmonary infection, however, were found among the rock workers of more than 15 years' service. The prevalence of pulmonary tuberculosis among the hard-coal mining employees at ages below 35 was slightly less than that found through studies of tuberculosis among male adults in the general population of the country. In the age group 35 to 44, however, the prevalence of tuberculosis was about twice, at ages 45 to 54 about 5 times, and for the ages above 55 it was about 10 times the rate found in the general population. TKe highest prevalence of clinical pulmonary tuberculosis occurred among the rock workers (men who had been employed in rock loading or rock extraction fur more than 2 or 3 years). After 20 years'serv ice, of which more than 2 or 3 years were in rock work, 37 percent presented evidence of pulmonary tuberculosis. In a group of 135 completely disabled former anthracite workers, which diil not include any known cases of tuberculosis, 10 percent proved positive for pulmonary tuberculosis. Pulmonary infection (tuberculous and nontuberculous) was found among 58 percent of the employed men having early antbreco-sUicosis, and in 92 percent of the workers in the more advanced stages. Clinical pulmonary tuberculosis was diagnosed ip 15 percent of those with early unthroco-silicoeis, and in 43 percent of those in the more advanced stages. ' In all groups combined, with the exception of the control group, about 20 percent of the nontuberculous workers were diagnosed as having some respiratory disease other than tuberculosis. In tbe control group only 6 percent bad nontuberculous respiratory disease. In the control group less than 2 percent were found with moderate or marked physical impairment causing decreuscd capacity for work as compared with about 10 percent among the regular miners, and with approximately 13 percent among the rock workers. With the exception of the rock workers, no gronp showed moderate or marked physical impairment in excess of that found among the controls when the period of employment was less than 20 years. However, an excess n Ittn v.iwtr'klrki'/*/* I'lirylftl lm wan rerrr n f uou err'^r'ir o (( 1469 Aug<ut to, was miners and among others exposed to dust containing less than 5 percent free silica when they had worked from 10 to 20 years in atmospheres containing more than 100 million particles per cubic foot. The correlations between exposure to dust and the evidence of constitutional changes left little doubt as to the etiological significance of the dust in the air breathed- lake correlations were found between the silica exposure and the extent of pulmonary changes. Mortality from respiratory diseases was found to be much greater among anthracite workers tillin' iu the general adult male population of the country. The data indicated that underground work in the absence of dust did not predispose to fatal attacks of respiratory disease. FREVKNTION OF SILICOSIS This phase of tbe silicosis problem may advantageously be consid ered under two main divisions--medical and mechanical. Medical.--Preliminary and periodic physical and roentgenological examination should be made of all employees engaged in industrial processes where there is a potential if not actual exposure to excessive concentrations of silica in the atmosphere. Medical personnel making these examinations should be familiar with the industrial processes in which the individual iu to be employed. In fairness to the individual, his fellow workers, industry, and even the public at large, an individual with evidence of active tuberculosis or extensive healed lesions should not be employed in an atmosphere where there may be exposure to silica dust. The infected individual's condition may become aggravated by such, exposure to silica dust; his fellow workers may become infected under conditions which might not be dangerous were it not for the presence of silica dust; industry may eventually bear tho burden of compensation for injury to tbe health of the employee and possibly some of hia coworkers; and fust, but not least important, tbe prevention and control of tuberculosis among the general population will be more difficult. In the absence . of infection, silicosis is a slowly progressing disease and develops at such a rate that tbe individual affected may not become disabled during his ordinary working life. Therefore, if infection can bo lessened, tbe silicosis problem may be much more readily controlled. Periodic physical examination will serve to detect early evidence of infection and abnormal pulmonuiy changes resulting from dust ex posure, which will permit correction of the conditions causing the pulmonary fibroma and prevent tbe development of disabling pulmo nary disease. Unless active pulmonary infection is diagnosed, the individual in whom a beginning fibrosis or nondisabling silicosis is present may be safety continued at his employment, provided the dustv rnnilltinna /iiciorr ?4 - i H-. ^ 1 * cr: '.j Y c IJ 4 ij 1r T 0. ( August iu was 1472 (IS) BlnoinfwVi, J. J.. ud Droeasen, W. C.: SilicootamongFinlte quurlen. Pub. Health Hup., 40 : 679 (1934). (77) ThoiuiiKoii, L. R., Bruneiage, D. K., Russell, A. E., and Bleoinfielil, J. J.: The IsaIUi o7 workers iu dusty trades. I. Health at workers in a Portland content plant. Pub. Health Bull. Na 170, D. 8. Public Health Service. Government Printing Office, Washington, D. C. (1028.) 7/S) Chapman, B. M.: Acute silicnsia J. Am. Med. Assoe., 98: 1430 (1932). (IS) Kessler, U. II.; Silicosis in the abrasive powder industry. 3. Am. Pub. Health Assoc., 21: 1300 (1031). (20) MacDonald, C., Piggnt, A. P., and Gilder, F. W.: Two eases of acute sili- co&w. Lancet, 2: 846 (1930). (81) Kilgore, E S.; Pbeuuvonueoniosis; An unusually acute form. J. Am. Med. Assoe., 99: 1414(1932). . ... (77) Kettle, E. H.: Action of benulul dusts, lust. Min. A Met., Bull. Nos. 357 and 368. (1934.) . (83) Gardner, L. EL: A pathological study of eight lungs from employees in the granite industry, fa reference 15, p. 138. (1929.) (87) lekert, Frans: Staublunge und Tuberkukmc. Big. d. Ges. Tuberk. Fareh., 3: 432 (1931). . ,,. (86) Lehmanu, G.: Die Funktiou der mcnachlichen Naae ais Staubfilter. At- beiUiihyidologfe,7: 167 (1933). {26) Suumiixrs, W. E.: Report of an investigation at Bendigo into the prevalence, nature, causes and prevention of miners' phthisis. Stillwell & Co., Mel- , bourne. (1907.) (97) Britten, R- H.: Occupational mortality among males in England and Wales, 1921-1923. A summary of the report of the Be&suar General. Pub. Health Rep., 43: 1565 (1928). (,_2_8,) Gardner, L. U.: Tuberculous infection ami tuberculosis as modified by ' experimentalpceuDionokooiaBUt. Tubercle, 6: 336, 443 (1925). (89) Irvine, L G.: The Chairman's speech. In Silicosis, Studies and Reports. Series F (Industrial Hygiene) No. 13. International Labour Office, Geneva. P. 18. (1930.) _ (50) Bokme-OMhui, A.: The prognosis of silicosis. Beitr. i. Klin. d. Tuberk. (1933.) (Reviewed in the 3. lnd. Uyg., Abstract Section, May 1934.) (51) Merewether, E. ft. A.; A memorandum on asbestosis. Tubercle, 15: 69 (1933). (Sgf Dreessen, W. C.: Effects of certain silicate dusts as the lungs. J. lnd. Hjg., 15: 66 (1933). STUDIES ON TBICIHNOSIS TU. The Past and Present Status ef Trichinosis in the United Sides, and the Indicated Central Measures 1 * * IV. V. VI. By Macwcs C. Haul,* On*/, IXeiritrn tf Zoology, National iariilufc qf Health, , United Slates Public Health Service introduction Some factors regarding trichinosis that have been clarified since the problem was token up by the Public Health Service in the spring of 1936 are as follows: 1. Abundant evidence indicates quite clearly that trichinosis is probably a greater problem in the United States than in any other country in the world. The evidence to this effect was available about 5<l years ago, but was quite generally overlooked, disregarded, or misinterpreted. Died Dr 1, IMS. ,1 ( 1473 input im 2. Human trichinosis rests primarily on a basis of swine trichinosis. 3. Swine trichinosis rests primarily on a basis of uncooked or in adequately cooked pork scraps fed to swine iu garbage, iutde scraps, swill, and similar material. 4. The indicated control of trichinosis in the United States is prima rily a matter of keeping such uncooked pork scrups out of the feed of swine, and either cooking such feed os garbage or refraining from feeding any food containing pork scraps. 5. Bats appear to have a very minor role in the production of porcine trichinosis, and at this time may be given only secondary consideration in our control measures. 6. The evidence available indicates that our too casual measures for the control of trichinosis have not lowered the incidence of trichi nae or trichinosis in man in this country during the past 60 years. The incidence in swine has decreased only to the extent that the once widespread practice of feeding offal from slaughtered hogs to other hogs lias decreased; and this bad practice has been almost entirely abolished purely as a result of improved sanitary conditions in general and not as a definite port of any trichinosis control program. 7. Prompt action looking towards the control of trichinosis is im perative for the protection of the public health on the one hand, and . the protection and improvement of the swine industry and the pack ing industry on the other band. An extension of the present move by scientists, physicians, and veterinarians to protect the public health must be anticipated by the swine growers and puckers to pro tect their industries from the consequences which may be exported from research within the next few years. The factors just enumerated will be discussed in the following sections. FKEVJJ.IvNCE 08 TRICHINOSIS There was abundant evidence 50 yearn ago that the United States had on extraordinary prevalence of trichinosis, but that evidence was misread, misunderstood, disregarded, or misinterpreted far the most part, and wholly unwarranted conehiaiona were drawn from it. Various writers, including Mark (i), pointed out, in the 1880'a, that 4 faUoirio art lto yamliin atlklas of tins uries: h Hit tocwteoca of IxicMaosis ai Indicated by post-mortem asaimlatrtWftis of 300 diaphragms. By Maurice O. {till wd H, J Cufliuk fob, UutU Sam K; (1907). (Reprint IftMJ H. Bona correlation ud faaplinUuiat in MuiMtiw with tin Imidcuta of tricttiao* found lo J0Q tlApkncm By Maurice C. Hull ajvtl II. J. Cottm. Fob. Benny Rep., 31: M3 (H0T7). (B print 1117.) Uf. The unpki cSloks) flriun o( bidtluulii, and tb (bscanii at UitdfawM. Rj Maurice O. UsklL Pub. Healtb Hep., B&S9 (1417). (Reprint tail) IV. XlMinlecrilbaBwbai^lulbueukUMprolucikm4dlMMUatflBbiM ByUainlceO.BkU. Pub. HatlthHep4n:VMWP). (RapriotUM.) V. Tba hachbiaco of tdctdbods m Indicated by post-mextern puitJimlitne ef ijOOQ dbiphn^nis. By M.7. Nobii aud Joha Bmiccfldi, Pub. HuHb Bcp^ B <IK (ISB). (Urpnut i9uV) VI. Kpddemlolecleol aspects ot Uicfalmwit in tbo Ualttfd Slates u faMlktlal bv an Tumliwilnn cf i a*