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FILE NAME Talc TALC DATE 1957 DOC TALC096 DOCUMENT DESCRIPTION Book Excerpt - The Physics and Chemistry of Dust REVIEW OF ANNUAL MEDICINE DAVID DAVID RYTAND, Editor Stanford University RYTAND RYTAND Editor WILLIAM CREGER Associate Editor Stanford University CREGER Associate Editor VOLUME 8 1957 ANNUAL REVIEWS . PALO ALTO, CALIFORNIA U.S.A. nificance lie others rise to the classical cent of only a few ree silica produces a result of the high ollagenous fibrosis Infection 24 The film on the surface 25 ganister bricks to ainly clay neither In this occupation interfered with the or the exposure to al silicosis amongst ave been described iosis and showing iners The average was very different pt when the lungs at some of the air- that the presence ant as it could de- ly the aluminium admixture of shale n its solubility ble to inert dusts Instituent of which we come to cases hemical combina- n enormous num- coniosis have been mstances are too ief difficulties are n free silica along complicates the osure to dust alline silicates in sed in various incates as colloidal resent in crystal- THE PHYSICS AND CHEMISTRY OF DUST 327 China clay or kaolin is a degradation product of granite and consists of up to 25 per cent of free silica mixed with hydrated aluminium silicate and traces of other elements A mortem examination of a man who had long been exposed to ball clay dust has been described by Thomas 29 who found silicotic nodules which were less whorled than is typical and had taken a very long time to develop another case also of long exposure is given by Bastenier 30 A survey of 31 pottery workers by Chiappa & Ferri 31 disclosed only a relatively benign silicosis The exposure of rats to the dust by intratracheal injection of saline suspension by King et al 32 revealed only phagocytosis with no fibrosis within periods of 60 to 161 days The free silica content of the kaolin was not determined but the silica solubility was very low It seems that kaolin is definitely not responsible for a fibrous silicosis like quartz and that cases in which fibrosis has been observed are a result of tuberculous involvement 30 33 of lungs heavily charged with dust or to the presence of quartz with its action modified by the kaolin which does not however inhibit the growth of fibrous nodules The comparative freedom from silicosis of men in the brick and tile industry handling china clays and fireclays containing free silica is commented on by Uytdenhoef 34 They inhaled dust containing 11 to 46 per cent of free silica in concentrations up to 700 particles per cc He suggests that the concentrations might have been below the danger level or that the aluminium silicates had an inhibitory effect selective sampling with determination of free silica in the respirable fraction should have been em- ployed Deaner 35 describes silicosis in fireclay miners with histological exam- ination of one case The man had worked for 23 years as a fireclay miner in a colliery where the clay was adjacent to the coal seam The clay was mainly aluminium silicate with only traces of iron calcium potassium and sodium but it contained a substantial amount of free silica Laminated fibrous nodules of classical silicosis were present in the lungs The occurrence of silicotic nodulation in this case and that of Thomas 29 argues against a specific inhibitory action by colloidal aluminium silicate which appears on its own to cause an inert dust type of pneumoconiosis Fuller's earth another clay is a hydrated alumino silicate containing iron It has been reported as causing pneumoconiosis 36 37 38 Quartz was present in these cases but the disease differed from classical silicosis and and took longer to develop The dust contains 50 to 60 per cent of combined silica i.e. SiO2 in silicates A number of cases of silicosis diagnosed by chest rays are described by Rombola & Guardascione 39 in the bentonite industry there had been very heavy exposure to dust This clay is mainly montmorillonite it contains a trace of quartz along with 32 per cent of amorphous silica plus betacristobalite There were no mortem findings to indicate whether the disease was correctly described as silicosis exemplified by the classical nodulation or whether there was diffuse fibrosis and to what extent The maximum exposure was seven years A dust containing 32 per cent of free - law Copyright U.S. by protected be may and party third a by Medicne of Library National the of colection the from copied was page this on material The 328 DAVIES crystalline silica inhaled in the concentration and particle size described would normally have been lethal in this time Peretti & Occella 40 suggest that the fibrogenic action of quartz is enhanced in the presence of certain clay hydrosilicates There appears to be no evidence for this statement either on physical chemical or clinical grounds The rapid onset of silicosis leading to death within a few years which was common in the days before precautions were taken among men quarrying sandstone shaping it or grinding upon dry sandstone wheels has no parallel in the exposure to silicates in clay or crystalline form even when an appreciable amount of free quartz is present The evidence is towards a diminution of the activity of quartz attributable rather to the presence of an inert diluent than to specific inhibitory action Pneumoconioses caused by inhaling dust from clays are essentially slow in developing even under quite dusty conditions : Occella 41 has analysed many industrial clays and has found free quartz present in proportions up to 50 per cent This figure did not always provide a good index of the hazard likely to be attributable to the material because a low concentration of quartz was often associated with a high pro- portion in the finer particles which alone were small enough to be retained in the lungs A survey of the cement clay and pottery industries by Sayers et al 42 showed the main hazards to be the known ones attributable to silica and lead A study by Parmeggiani 43 based on mass radiography of workers in the cement industry proved that the highest incidence of pneumoconiosis was amongst those employed in mines and quarries where raw materials were obtained and cement dust was absent Few workers in the factory where cement was made showed more than slight lung shadows This was confirmed by Giulani & Belli 44 who rayed 180 people working in a cement factory and found no cases of silicosis although 20 per cent of them gave indications of inert dust deposits Upper respiratory disturbances were prevalent confirming that industrial hygiene practice should not be restricted to eliminating fine respirable dust Russell 45 also observed the tendency of cement dust to cause bronchitis but found no encouragement of tuberculosis and only slight pneumoconiosis Experiments in which rats inhaled dust of Portland cement containing less than 1 per cent of free silica revealed no fibrotic changes 46 Miller & Sayers classed Portland cement as an absorptive dust when tested by peritoneal injection since the initial lesion dispersed and the dust disap- peared 103 NONFIBROUS CRYSTALLINE SILICATES Passing on to the crystalline silicates several papers have been published on exposure to dust of the felspars These comprise two similar groups of hydrous alumino of alkalis and alkaline earths crystallising isomorphously in monoclinic and triclinic forms Copyright oN Experim in saline than quart three kinds with time nique was may and party third by Medicine of Library National the of colection the from menting w copied granite dus however was page this on material The THE PHYSICS AND CHEMISTRY OF DUST 329 ticle size described tion of quartz is enhere appears to be hemical or clinical within a few years taken among men adstone wheels has ne form even when idence is towards a to the presence of | moconioses caused loping even under Experimenting by the intratracheal injection into rats of dust suspensions in saline Mohanty et al 47 found that felspar was very much less fibrogenic than quartz Policard & Collet 48 confirmed this work they compared three kinds of felspar and obtained varying amounts of fibrosis increasing with time but always less intense than was produced by silica Their tech- nique was the intraperitoneal injection of saline suspensions Klosterk^tter & J^tten49 using intratracheal injection found only slight fibrosis from a potash felspar hornblende another complex crystalline silicate gave none Rotter & G^/rtner 50 describing a fatal human case with extensive tuberculosis state that the nodules were not like those of silicosis being more widely disseminated there was also less increase in reticular fibres and collagenous tissue The dust inhaled by the victim contained 38 to 45 per cent of quartz with many particles smaller than 5 ...they supposed the | aluminium potassium sodium and calcium ions which would leach out into nd has found free solution had exerted a neutralizing effect ure did not always . Granite consists of about thirds felspar with third and le to the material | quartz mica it contains small amounts of iron magnesium calcium etc. Silicosis ed with a high pro- with nodulation is produced in men exposed to the dust but there is more ugh to be retained tendency to diffuse fibrosis than with straightforward silicosis The condi- y Sayers et al 42 utable to silica and graphy of workers of pneumoconiosis ere raw materials the factory where his was confirmed 1 a cement factory n gave indications ere prevalent conricted to eliminat- ndency of cement tuberculosis and ement containing ges 46 Miller & when tested by 1 the dust disap- tion is progressive and associated with tuberculosis which causes the deaths but a much longer exposure is required than would be the case with pure quartz dust These conclusions were reached following exhaustive studies of granite workers in Vermont 51 52 A survey of 355 stonemasons in Australia who worked on sandstone 90 per cent free silica granite 30 per cent free silica and limestone non- siliceous revealed seven cases of silicosis in sandstone workers and one in a granite mason Seventy cases of moderate diffuse fibrosis were seen without incapacity and the amount of lung damage was judged to be pro- portional to the free silica content of the stone worked 53 In France exposures of up to seven years to very high concentrations of granite dust produced while tunnelling through rock containing 18.4 per cent of free silica failed to cause silicosis 54 Surveys of the Austrian and German granite industries led R^hrlto conclude that compensatable silico- sis was caused only after breathing the dust for many years 55 Experimenting with rats by intratracheal injection of saline suspensions of Cornish granite dust King et al produced focal nodulation in 100 days The nodules however contained only a tangled reticulin network without collagen and men did not progress up to 250 days 56 FNS Kaolin is derived from granite and reviewing the evidence relating to FRET ; kaolin felspar and granite together it is fairly clear that these substances ve been published similar groups of crystallising iso- produce silicosis when inhaled as dusts by virtue of their content of free silica It is also very doubtful if any inhibitory action can be ascribed to these minerals in respect of the fibrogenic property of free silica There is no doubt that fibrous nodulation in human lungs results from the inhalation of the dusts and that the aluminium silicate which they contain does not prevent Pe 330 DAVIES it Some degree of modification of the nodule the presence of diffuse fibrosis and the long duration of exposure required all seem factors which can be accounted for by the dilution of active siliceous dust by inert silicates A method of assessing the silicosis risk attributable to dust made from particular rock was proposed by Landwehr 57 A danger figure was attribu.ed to each mineral constituent of the rock and multiplied by the weight page present The products for all the constituents were then summed and the total was multiplied by a fraction representing the percentage of fine dust wwaaswass generated by drilling No account was taken of constituents which could suppress fibrogenic activity nor of the fact that the danger of a mineral copied migh be a result solely of its quartz content felspar for example was rated from as 70 per cent as dangerous as quartz A scheme of this nature suffers from from the limitation that the effects of quartz are different from those of other from rocks which makes it rather misleading to classify them together Land- the wehr s treatise contains useful information about a number of rocks colection The olivines orthorhombic silicates of magnesium and ferrous iron appear to provoke little fibrosis in the lungs Experiments on rats by King colection et al 58 using intratracheal injection of saline suspensions revealed phago- of cytosis with the alveolar walls thickened because of congestion of the lym- the the phat cs by dust containing macrophages Slight fibrosis was present in the alveclar walls but there was no organized focal nodulation These minerals National are used as a substitute for siliceous sand in various industries and have contributed to the decline of silicosis Sericite a muscovite or potash mica is an alteration product of felspar Some historical interest attaches to sericite because Jones 59 claimed that it was the cause of silicosis His argument was based upon his discovery in the lungs of silicotic miners of large numbers of fine needles of sericite under 2 ... in length quartz particles were also present but in numbers subordinate to sericite Evidence against this theory was put forward 60 to 63 and both Lemon & Higgins 64 and King et al 65 found that sericite produced a minimal tissue response when injected into rats lungs appreciable fibrosis was evoked if the dust was treated with hydrochloric acid before injection though anomalies between solubility and pathological effect were observed Lanc wehr 66 claimed sericite to be harmless on its own but to act as a party catalyst and to enhance the danger of quartz his evidence for this statement is not clear Support for Landwehr's hypothesis is found in papers by Weiland 67 and by Hurlbut & Beyer 68 The experiments of the former on guinea pigs seem to have been confused by intercurrent disease The latter compare two foundries one with many cases of silicosis and the other with none While associating the disease with the sericite content of a part- ing powder used in the bad foundry and even commenting on the fact that protec d the castings which it turned out possessed a finer finish than those from the other they entirely fail to record any details of the fettling processes or US measurements of dust concentrations during this operation which was obviously prosecuted more vigorously in the foundry with the high incidence of Copyright Copyright Copyright Copyright law THE PH disease The fettling of It is difficult to credit of quartz within the lu An examination of quartz and felspar with cosis only amongst me could be ascribed to m mines but this was pro drillings to an extent t Sericite and mica fr dusts in pneumoconio inhibitory action can b ence in the slate indust ble to the silica conter and mica The first wo content is high 35 per carried out by Wade ( where the free quartz workers in slate which being largely sericite Italian slate also cont 8.6 per cent ray pl slate revealed initial s ment silicosis and tu The diseases had thus The suggestion that sis because the particl an exaggerated incide velopment of disease tainly no gross effect quartz dust This su Bruckmann 76 on t tale platelets in lung be accounted for by quartz and Canada b particles in Canada ba microscopy of the lu size must be subject t Many silicates cry longer fibres the latt asbestos the fibres c tudinally an indefinit Sillimanite an ant ce of diffuse fibrosis actors which can be 7 inert silicates o dust made from a inger figure was atiplied by the weight n summed and the centage of fine dust ituents which could anger of a mineral example was rated _ nature suffers from from those of other em together Land- mber of rocks and ferrous iron ap- its on rats by King ons revealed phagongestion of the lym3 was present in the tion These minerals istries and have con- 1 product of felspar 3 59 claimed that it his discovery in the of sericite under 2 ibers subordinate to 60 to 63 and both . sericite produced a . appreciable fibrosis acid before injection effect were observed own but to act as a dence for this state3 found in papers by ments of the former current disease The licosis and the other te content of a part- ting on the fact that than those from the fettling processes or ion which was obvithe high incidence of law Copyright THE PHYSICS AND CHEMISTRY OF DUST 331 disease The fettling of castings is the principal cause of silicosis in foundries U.S. It is difficult to credit the theory of Hass 69 that sericite is formed out of quartz within the lungs by An examination of men working with mica and pegmatite a mixture of protected quartz and felspar with some mica by Dreessen et al 70 revealed true sili- cosis only amongst men exposed to quartz though effects were seen that could be ascribed to mica dust Silicosis has been reported in the Bihar mica mines but this was probably a result of free silica which was present in rock be may drillings to an extent between 11 and 67 per cent 71 Sericite and mica frequently accompany silica in silicotic lungs and other dusts in pneumoconiotic lungs and it is improbable that any appreciable and party inhibitory action can be ascribed to them This view is supported by experi- ence in the slate industry where the danger of the dust is probably attributa- third ble to the silica content and is not greatly influenced by associated sericite and mica The first work on exposure to slate dust in Wales where the silica a content is high 35 per cent and there is a long history of tuberculosis was by carried out by Wade 72 Silicosis was detected in Australian slate quarries Medic ne where the free quartz content was 33 per cent 73 In France however workers in slate which had a free silica content of only 7 per cent the rest being largely sericite showed few signs of respiratory impairment 74 of Italian slate also contains a low percentage of quartz ranging from 2.8 to Library 8.6 per cent ray photographs of personnel engaged in working Ligurian slate revealed initial signs of pneumoconiosis after 10 to 15 years employ- National ment silicosis and tuberculosis existed only in men who had retired 75 The diseases had thus required a full working lifetime for their development The suggestion that micaceous minerals are liable to cause pneumoconio- sis because the particles are flat lamellae does not seem to be borne out by the an exaggerated incidence of disease or by a particularly rapid rate of de- of velopment of disease amongst persons exposed to mica dust There is cer- tainly no gross effect comparable with the vicious attack from crystalline quartz dust This suggestion has however been made by Landwehr & colection Bruckmann 76 on the basis of a lack of quartz and an excess of mica and the talc platelets in lung sections seen under the microscope Their result may be accounted for by the small difference between the refractive indices of from quartz and Canada balsam which makes the identification of small quartz copied particles in Canada balsam mounts a difficult matter Any estimate by visual microscopy of the lung content of dust in particles of the order of 1 in size must be subject to considerable uncertainty was FIBROUS CRYSTALLINE SILICATES page Many silicates crystallise in fibrous form both as short spicules and in this longer fibres the latter may be either brittle or else silky and flexible like on asbestos the fibres of which also possess the property of cleaving longi- tudinally an indefinite number of times Sillimanite an anhydrous aluminium silicate used for special purposes in material The - The material on this page was copied from the colection of the National Library of Medicne by a third party and may be protecd by U.S. Copy 332 DAVIES the pottery industry crystallises in hard acicular crystals which do not cleave but are readily ground to powder Middleton 77 stated on limited evidence that the dust did not appear to be highly dangerous but it was later held responsible for lung fibrosis including nodulation in men engaged in making artificial corundum by heating bauxite and kaolin in an electrical furnace 78 79 When rabbits were exposed to airborne sillimanite dust fibrosis of the lungs with some nodulation was observed 80 Other reports of bauxite fume pneumoconiosis suggest that it is caused by the inhalation of extremely high concentrations of colloidal silica aerosol and that the presence of sillimanite in the fume is incidental The end result in these cases was diffuse interstitial fibrosis without nodulation deriving from interference with the koniophage clearance mechanism by the large quantity of dust present in the lungs and the high solubility of colloidal particles of silica 81 to 84 King et al 85 however have produced a dense collagenous fibrosis in the lungs of rats by administering large quantities of colloidal alumina Al2O3 Sepiolite or meerschaum a light hydrated magnesium silicate resembling cuttle bone and containing both fibrous crystals and amorphous material has been cited in one case as a cause of silicatosis 86 the ray pictures show diffuse shadowing The association of the shape of inhaled dust particles with disease is particularly interesting in the case of talc a hydrated magnesium silicate forming monoclinic crystals which are soft and cleave into small scales and spicules Dreessen & Dallavalle found that Georgia talc a hydrous magnesium silicate containing 20 to 30 per cent of dolomite and 10 per cent of tremolite was more injurious than tremolite talc 87 88 though the damage caused was in no way comparable with that attributable to silica dust The Georgia talc contained many fibrous splinters and aggregates and was composed of hydrous magnesium silicate Tremolite is a hydrous calcium magnesium silicate which occurs both as slender blade prisms and as silky fibres Hogue & Mallette 89 after examining rubber workers exposed to pure talc containing neither fibrous varieties nor free silica decided that this substance did not produce pathological changes in the lungs but emphasized that the term tale was used commercially in a wide sense to include tremo- lite pyrophyllite and even quartz Massive lung shadowing in miners of pyrophyllite a hydrated aluminium silicate similar to talc and occurring in foliated lamellar and somewhat fibrous masses was observed by Eason et al 90 but the dust contained from 25 to 35 per cent of free quartz Porro et al 91 found pneumoconiosis in tremolite workers whose lungs exhibited fibrosis and contained talc bodies resembling asbestos bodies when examined mortem That the fibrous varieties of talc produce a disease analogous to asbestosis with diffuse fibrosis and asbestos bodies is confirmed by Siegal et al 92 and by Greenburg 93 THE PI Several other case dust and diagnosed by without reference to t scribes a generalized which contained less from the sharp spicule had been 24 years e which with the ray pneumoconiosis McLaughlin et al lungs of a worker in carditis Although the for 33 years contained to 10 ...in length wer in the root nodes but more numerous in the characteristic pattern fibrous particles and found in cases of asb Rapid developme similar to silicosis in is described by Alivis up to 1,925 particles count for pronounced unless a fair proportio is given on this poin Miller & Sayers ( lowing the intraperit and soapstone 65 F therefore classed the borne talc dust wh bronchial reactions a but the animals were enough for it to be re skin and peritoneum Asbestos shares 1 years a high degree The disease asbesto occurrence was held 110 Its associatio sis though this is 1 Germany 111 Per contracting cancer c served with other p Asbestosis differ ystals which do not 7 stated on limited ngerous but it was ion in men engaged aolin in an electrical dust fibrosis of the orts of bauxite fume on of extremely high esence of sillimanite , was diffuse inter- erference with the ' of dust present in of silica 81 to 84 lagenous fibrosis in f colloidal alumina silicate resembling morphous material ; the ray pictures cles with disease is magnesium silicate to small scales and ydrous magnesium er cent of tremolite the damage caused dust The Georgia id was composed of calcium magnesium and as silky fibres ers exposed to pure ecided that this sub- gs but emphasized se to include tremo- lowing in miners of alc and occurring in rved by Eason et al f free quartz Porro 1ose lungs exhibited dies when examined a disease analogous confirmed by Siegal THE PHYSICS AND CHEMISTRY OF DUST 333 Several other cases of pneumoconiosis caused by long exposure to talc dust and diagnosed by ray as differing from silicosis have been reported without reference to the shape of the particles 94 to 99 Millman 100 describes a generalized pneumoconiosis from exposure to talcum powder dust which contained less than 0.5 per cent of free silica and was entirely free from the sharp spicules found in the fibrous variety of tremolite talc There had been 24 years exposure a long period to high dust concentrations which with the ray reproduced suggest this to be a case of inert dust pneumoconiosis McLaughlin et al 101 made a very thorough examination of the lungs of a worker in a rubber tyre factory who died of rheumatic endocarditis Although the Norwegian talc dust to which he had been exposed for 33 years contained both platelet and fibrous particles only the latter up to 10 ... in length were recovered from the lungs Fibrosis was not observed in the root nodes but was scattered throughout the lung in small nodules more numerous in the lower lobes which were less compact and lacked the characteristic pattern of silicotic nodules These nodules were packed with fibrous particles and contained curious bodies somewhat similar to those found in cases of asbestosis There had been no exposure to asbestos Rapid development of talc pneumoconiosis clinically and radiologically similar to silicosis in workers exposed to very heavy concentrations of dust is described by Alivisatos et al 102 No free silica was present Dust counts up to 1,925 particles per cc are quoted this would not be adequate to account for pronounced ray shadowing in periods as short as 16 to 60 months unless a fair proportion of long fibrous particles was present No information is given on this point Miller & Sayers 103 obtained only an initial foreign body reaction fol- lowing the intraperitoneal injection of talc 75 per cent fibrous tremolite and soapstone 65 per cent fibrous tremolite dust into guinea pigs and therefore classed them as inert while Policard 104 exposing rats to airborne talc dust which contained shaped particles observed only bronchial reactions and loss of mobility of phagocytes No fibrosis was found but the animals were killed off after 20 days which may not have been long enough for it to be recognised In the human subject talc granulomata of the skin and peritoneum have been described 105 to 109 Asbestos shares with quartz the capacity for producing rapidly in a few years a high degree of fibrosis of the lungs when inhaled as airborne dust The disease asbestosis was first recognised in 1906 and an inquiry into its occurrence was held by the Factory Department of the Home Office in 1928 110 Its association with tuberculosis is infrequent compared with silicosis though this is less marked in England than in the United States and Germany 111 Persons affected with asbestosis have an increased risk of contracting cancer of the lung 112 113 a tendency which has not been ob- served with other pneumoconioses 114 115 116 Asbestosis differs from silicosis in additional ways It does not progress law Copyright U.S. by protected FePajeg be seahgim may mat and party third a by Medicne of Library National the of colection the from copied was page this on material The The material on this page was copied from the colection of the National Library of Medicne by a third party and may be protected by U.S. Copyright law 334 DAVIES after exposure to the dust has ceased and it is characterised by diffuse ray shadowing as a result of pulmonary fibrosis which unlike silicosis chiefly affects the bases of the lungs spreading to the middle and upper parts as the disease advances with the apices usually clear The laminated fibrous nodules of silicosis do not grow as a result of the presence of asbestos in the lungs instead a diffuse general fibrosis without calcification is stimulated Characteristic asbestos bodies are found in the fibrous tissue air spaces and sputum and within macrophages they consist of asbestos fibres sheathed with containing protein derived from the capillary exudate They were first observed in the lungs of an asbestos worker in 1927 similar objects have since been found in cases of talc graphite carborundum and coal pneumoconiosis and possibly byssinosis Asbestos bodies may be up to 250 ...long ultimately they appear to break up and disperse 117 118 119 Injection of asbestos bodies into the peritoneum of guinea pigs failed to provoke the fibrous reaction observed with naked fibres 124 Miller & Sayers 103 however found asbestos fibres to be inert by a similar technique Asbestos fibres produce granulomata of the skin or asbestos corns 120 121 122 which do not contain asbestos bodies An immediate inflammatory reaction in the peritoneum of mice has been caused by fibres detached accidentally from an asbestos sterilizing filter talc acted similarly but glass fibres and mica produced only a slight response with no immediate effect from silica 123 possibly because the particles were too coarse 140 mesh Histologically the characteristic feature of asbestosis is the growth of fibrosis around the fine bronchioles and alveolar ducts suggesting that asbestos fibres lodge across air channels which are of appropriate diameter and work into the surrounding tissue by virtue of its movement during respiration This has been supported by the results of many animal experiments at Saranac by L. U. Gardner which have been reported by Vorwald et al 124 These showed that peribronchiolar fibrosis could be produced in guinea pigs cats and rats by inhalation of asbestos dust containing fibres around 10 ...in length No effect was produced in mice Inhalation of dust almost free from long fibres produced little fibrosis Further experiments by intratracheal injection of long and short fibre dusts using various kinds of mineral were carried out Using fibres 20 to 50 ... long it was shown that chrysotile amosite crocidolite tremolite and brucite were active for some reason anthophyllite was not Brucite is a fibrous form of magnesium hydroxide which is free from silica Glass wool of the same length and 3 in diameter produced no fibrosis When the dusts were ground before administration so as to break up the long fibres into pieces 3 and less in size no fibrous reaction was produced by any of them the only effect observed was a greater or lesser inflammatory reaction with transport by phagocytes to the lymphatics The association is with the fibrous habit of the mineral not with its crystalline form chrysotile is probably rhombic amosite is orthorhombic crocidolite and tremolite are monoclinic and brucite belongs to the rhombohedral section of the hexagonal systems Anthophyllite is orthorhombic THE PJ All these minerals be growth along a partic of their formation ma repeated longitudinal and his colleagues cc cleaving fibres of glas and his workers cli venous and intraperit Quartz particles be in various organs suc hyalinised fibrotic no ground to particles st jections of the short fit excited by inert dusts ing anthophyllite gav It is also claimed spleen did not cause a and peritoneum are m tissues Full details of Further evidence . is afforded by their ob inhibit asbestosis w aluminium had no inl quartz 126 127 alth Observations on t chanical factor in its of asbestosis in a ma of particles up to 4,0 were no localised nodi in the lower parts of e isolated and in group lungs but also in the Cartier describin states that all cases duration to concentr chrysotile asbestos fil 250 -- long This con be required to cause s of the figure associate of exposure Other c appeared to be harm Asbestosis from F by Noro 131 Fibres the fibres being most fibres up to 65 long Dreessen et al 1 ised by diffuse ray like silicosis chiefly and upper parts as e laminated fibrous ce of asbestos in the cation is stimulated us tissue air spaces estos fibres sheathed exudate They were 927 similar objects orundum and coal es may be up to 250 rse 117 118 119 ea pigs failed to pro24 Miller & Sayers nilar technique asbestos corns 120 ediate inflammatory ibres detached acci- similarly but glass no immediate effect coarse 140 mesh is is the growth of suggesting that aspropriate diameter ; movement during any animal experiported by Vorwald could be produced os dust containing mice Inhalation of sis Further experilusts using various u long it was shown ite were active for form of magnesium ame length and 3 ground before ad3 ...and less in size nly effect observed port by phagocytes neral not with its ce is orthorhombic ngs to the rhombo^ is orthorhombic THE PHYSICS AND CHEMISTRY OF DUST 335 All these minerals because of an enormously exaggerated rate of crystal growth along a particular axis being encouraged by conditions at the time of their formation may occur in the form of long fibres which are capable of repeated longitudinal subdivision It is this growth habit which Vorwald and his colleagues correlate with the power to produce asbestosis noncleaving fibres of glass of similar length do not cause the disease Vorwald and his workers clinch their argument with observations following intra- venous and intraperitoneal injection Quartz particles below 3 M in size when injected into the veins collected in various organs such as the liver and spleen and caused the growth of hyalinised fibrotic nodules of characteristic type The asbestos minerals ground to particles shorter than 3...produced no effect Intraperitoneal in- jections of the short fibre dusts caused only the phagocyte reaction commonly excited by inert dusts with no fibrosis Long fibre asbestos minerals includ- ing anthophyllite gave rise to fibrosis It is also claimed that direct injection of long asbestos fibres into the spleen did not cause asbestosis because this organ is static whereas the lung and peritoneum are mobile which makes the ends of the fibres work into the tissues Full details of this experiment are lacking from the paper Further evidence in favour of mechanical rather than chemical action is afforded by their observations that colloidal aluminium hydroxide did not inhibit asbestosis while King et al 125 found similarly that metallic aluminium had no inhibitory effect These substances prevent fibrosis from quartz 126 127 although an exception has been mentioned by King 128 Observations on the disease in humans confirm the existence of a me- chanical factor in its origin A typical case is described by Luton et al 129 of asbestosis in a man who died after 18 years exposure to concentrations of particles up to 4,000 per cc containing fibres up to 10 ...in length There were no localised nodules in the lungs but a general thickening of the pleura in the lower parts of each lung was evident Many asbestos bodies were seen isolated and in groups and dust particles could be traced not only in the lungs but also in the vessels of the liver kidney and spleen Cartier describing conditions at the Thetford mines in Canada 130 states that all cases of asbestosis arose from exposures of over 14 years duration to concentrations exceeding 18 particles per cubic centimetre of chrysotile asbestos fibres which were dry partially cleaved and from 10 to 250 ...long This concentration is of the order of tenth of what would be required to cause silicosis from quartz dust and less than hundredth of the figure associated with an inert dust pneumoconiosis in the same period of exposure Other dust consisting mainly of powdered serpentine rock appeared to be harmless Asbestosis from Finnish amphibole a hard brittle variety is described by Noro 131 Fibres and asbestos bodies were found in the lungs of victims the fibres being mostly 9 or less in length and under 1 ... in diameter a few fibres up to 65 ...long were seen Dreessen et al 132 in an exhaustive study of an asbestos textile in- law Copyright U.S. by protected be may and party third a by Medicne of Library National the of colection the from copied was page this on material The 336 DAVIES The dustry where the risk of asbestosis is much greater than in mining found airborne fibres of a median length ranging from 7 to 163 ...Asbestosis was material diagnosed in many workers and asbestos bodies were found in the lungs Dreessen and his colleagues comment on the very low dust concentrations which could be held responsible for causing the disease Concentrations below on 180 particles per cubic centimetre measured with a Konimeter were sug- this gested as being safe as no attempt was made to distinguish between fibrous and nonfibrous particles this does not necessarily conflict with Cartier's page figure given above The asbestos was mainly chrysotile was Alden and Howell 122 describe corns produced in 99 out of 167 workers with amosite No asbestosis was detected but figures for the airborne dust copied concentration are not included These facts do not oppose the theory that asbestosis is caused by fibres from penetrating the tissue of the primary lung lobule in the airways of which they are held up on account of their length it is also conceivable that easy the longitudinal cleavage of the fibres which results in fraying of the broken ends may be a necessary physical factor additional to a length exceeding colection 10 ...In spite of the failure of aluminium to inhibit fibrous growth however the possibility of a specific chemical reaction at the ends of the fibres cannot be excluded of the Asbestos bodies provide visual evidence of chemical action against the invading fibres probably to render them innocuous with special activity at National fractured ends The ultimate development of cancer cannot readily be accepted as resulting from mechanical stimulus or the presence of fibrous tissue without postulating some accessory cause The asbestos corn stimu- Library lated by small slivers penetrating the skin of the hand under which a fibrous response is initiated seems to be more specific than a foreign body reaction of The handling of glass wool slag wool and even glass fabrics causes skin irri- Medic ne tation because of the pentration of glass fibres but corns are not produced nor is there evidence of pneumoconiosis although long exposures have not yet been recorded 133 134 135 Finally Kettle 25 injected ground as- by bestos into subcutaneous connective tissue and produced active lesions a like those attributable to silica third In considering the reaction of tissue to dust both the immediate inflam- matory reaction and the term fibrotic effect have to be differentiated party Regarding the latter asbestos and talc dusts appear to be selective in respect and of both the organ and the species of animal which is not the case with quartz Quartz dust provokes a fibrogenic reaction with only minor dif- may ferences between species in every organ capable of retaining particles and be in every kind of animal which has been investigated 136 137 Miller & Sayers 103 found no fibrosis in guinea pigs injected intraperi- protec d toneally with asbestos and talc Gardner 136 obtained only a very slight effect in the lungs of mice and dogs with asbestos while man guinea pig cat and rat developed fibrosis He inoculated the dog by intratracheal injection by of a suspension of long chrysotile fibres in saline which failed to produce more U.S. Cop THE PH than minute granulom tion was continued for asbestos bodies were i phagocytosis over a p Yet the dog can e which had inhaled dust were handled The lun considerable diffuse i Asbestos bodies were These variations ir doubtful if they are g fibrous growth to be stimulating agent and this contact is mecha when they are admin uncertain than is the The relationship of produced by the injec fibrosis also requires c to subcutaneous injec and the ultimate dev lesions from the solut collodion bag of silica It is doubtful if th erating silicotic nodul perimenters disregar nodule which is evide referred to above 25 scars Complete disregar least in the case of as is progressive There connective tissue und PHYSICAL A The difference be difference between th focal collections of la gether from the distr of the air spaces in t tivity and lymph cur particles cannot harr cepted It is physically im by a single phagocyt an in mining found 63 ...Asbestosis was found in the lungs dust concentrations oncentrations below onimeter were sug- uish between fibrous 1flict with Cartier's 9 out of 167 workers or the airborne dust is caused by fibres e airways of which nceivable that easy ying of the broken a length exceeding Is growth however of the fibres cannot action against the 1 special activity at not readily be ac- sence of fibrous tisDestos corn stimu- der which a fibrous eign body reaction ics causes skin irri- are not produced exposures have not njected ground asced active lesions immediate inflam> be differentiated selective in respect not the case with h only minor dif- ning particles and , 137 injected intraperionly a very slight n guinea pig cat tracheal injection d to produce more THE PHYSICS AND CHEMISTRY OF DUST 337 than minute granulomata in peripheral lymphoid tissue although observation was continued for two years Inhalation was employed for the mouse asbestos bodies were formed but the tissue response remained limited to phagocytosis over a period of two years Yet the dog can experience asbestosis for Schuster 138 describes one which had inhaled dust for 10 years in a factory where three kinds of asbestos were handled The lungs contained fibres from 8 to 60 long and there was considerable diffuse interstitial peribronchiolar and perivascular fibrosis Asbestos bodies were absent These variations in the response to asbestos fibres are peculiar and it is doubtful if they are genuinely a result of differences of susceptibility For fibrous growth to be initiated contact must be established between the stimulating agent and an area of connective tissue It is conceivable that this contact is mechanically uncertain in the case of long fibres especially when they are administered by the injection of a liquid suspension more uncertain than is the case with granules of quartz The relationship of the immediate inflammatory reaction which is often produced by the injection of foreign material into tissue to the long term fibrosis also requires consideration Kettle 139 describes a tissue response to subcutaneous injections of colloidal silicic acid which included necrosis and the ultimate development of a fibrous scar He also produced similar lesions from the solution of silicic acid which leached out of a permeable collodion bag of silica embedded in tissue It is doubtful if these lesions can be regarded as analogous to the proliferating silicotic nodule Gardner Miller & Sayers and other more recent experimenters disregard any initial reaction and concentrate on the growing nodule which is evident only after a period of weeks Kettle's asbestos lesions referred to above 25 may come into the same category as his silicic acid scars Complete disregard of the variable initial reaction seems unjustified at least in the case of asbestos because it is doubtful if asbestosis in humans is progressive There may be a similarity between the asbestos scar in the connective tissue under the skin and the lung condition of asbestosis PHYSICAL AND CHEMICAL FACTORS IN PNEUMOCONIOSIS The difference between silicosis and asbestosis arises from the physical difference between the two dusts which cause them Silicotic nodules are focal collections of large numbers of particles which have been gathered to- gether from the distributed sites of their original deposition upon the walls of the air spaces in the lungs The focalisation is a result of phagocyte activity and lymph currents and it is necessary to postulate that the silica particles cannot harm the phagocytes appreciably if this description is accepted It is physically impossible for a long fibre over about 20 ...to be engulfed by a single phagocyte hence the building up of focal aggregations of such law Copyright U.S. by protected be may and party third a by Medicne of Library National the of colection the from copied was page this on material The The The material on this page was copied from the colection of the National Library of Medicne by a third party and may be protecd by U.S. Cop 338 DAVIES fpuarsteicles cannot take place and the fibrosis which they produce must be dif- Normally particles over 5 or 10 ...in size are not admitted to the fine bronchioles and alveoli since they impinge or settle under gravity upon Hence the viscous drag of the air upon their they move relative to the air is surface which is set up when a strong tendency to travel with abnormally large They possess therefore an air stream which explains the in lung tissue of asbestos fibres up to 250 ...long occurrence Asbestosis has been described as a disease of the silicosis as a disease of the lymph node It is primary lobule with eralisation and say that both correct to go beyond this gen- agent must establish are diseases of connective tissue The fibrosing fibres In the contact with tissue capable of producing collagen case of asbestosis this is the lymphoid tissue of the lobule the distribution of which has been described primary case of the asbestos corn it is the by Miller 140 in the perimental connective tissue beneath the skin In ex- pneumoconiosis it is the connective tissue of the with fibrogenic particles organ inoculated The inhalation of asbestos dust results in the nodes of all particles small accumulation in lymph enough to have been phagocytosed Mild fibrous fibre length increases above 5 The electron microscope has revealed that microscopic network of connective tissue contains a collagen fibrils along with intercellular material growth mechanism common to all species It is still obscure how the can stimulate the presence of silica particles in connective tissue The resulting fibrogenic nodules cells to produce collagen at an abnormal abnormal rate are similar to those of tuberculosis 144 and there TH must be some fea quartz and the tul occupations was o perimental increas colloidal solution c Gye & Purdy ( ministered parente by a deposit of col of silicic acid fro growth It could + from the colloidal of blood and depc would initiate coll This view pers 148 was one of : growing silicotic n formation of scar t showed that nodu tion he repeated K into tissue and fai ticulate silica cau phagocyte changir The solubility served decrease in of iron 25 or alu cement 126 127 There was som though exceptions to produce silicosi by another consti were accepted as e It was also four with their solubili direct and unspeci sulting fibrous gro The grounds f silica and silicate t collagen productic no positive eviden cutaneous injectio doubtful because o but contained area the toxic action of effect Necrosis in sequent to it produce must be dif- idmitted to the fine under gravity upon excreted Fine fibres n compact granules hich is set up when y possess therefore plains the occurrence primary lobule with go beyond this gentissue The fibrosing producing collagen issue of the primary Miller 140 in the eath the skin In exthe organ inoculated umulation in lymph cytosed Mild fibrous es are caught in the talc fibrosis reported etween the complete ffuseness of asbesto- 11 scattered nodules up to 10 ...long but robably the greatest definition and large of transport as the ive tissue contains a Intercellular material n by which the cells granules 142 con- e involved and may led by van der Waals cules 143 separation of about gin a fact which cor- cosis and suggests a ; in connective tissue at an abnormal rate osis 144 and there THE PHYSICS AND CHEMISTRY OF DUST 339 must be some feature in the chain of causation common to the crystal of quartz and the tubercle bacillus The association of tuberculosis with dusty occupations was observed before the identification of silicosis and the ex- perimental increase of the local reaction to tubercle bacilli in the presence of colloidal solution of silica itself toxic 145 is well established 146 147 Gye & Purdy 145 showed that the tissue change induced by silica sol administered parenterally consisted of a slow thickening of capillary boundaries by a deposit of collagen and their work encouraged the theory that solution of silicic acid from quartz particles in the lymph tissue initiated fibrous growth It could equally well be argued that silica would be precipitated from the colloidal solution owing to its particles aggregating at the low pH of blood and depositing in the connective tissue irrigated by the capillaries would initiate collagenous growth near their walls This view persisted for 30 years in spite of certain difficulties Banting 148 was one of the first to distinguish clearly the peculiar nature of the silicotic nodule as distinct from the local toxic action necrosis and growing of colloidal silica sol He formation of scar tissue which followed the injection showed that nodules could be produced only by particulate silica in addi- tion he repeated Kettle's experiment of implanting a permeable bag of silica into tissue and failed to obtain nodules Banting's conclusion was that par- ticulate silica caused silicosis and that fibrosis might be initiated by the phagocyte changing from an amoeboid to a connective tissue cell The solubility theory persisted nevertheless with support from the ob- served decrease in silica solubility caused by the presence of small amounts of iron 25 or aluminium and of larger quantities of calcium hydroxide or cement 126 127 or by the presence of other rock dusts 128 There was some evidence of a parallel diminution of fibrogenic action though exceptions were noted Reports of siliceous dusts which were failing to produce silicosis were accounted for by the assumption of a depression by another constituent of silica solubility as mentioned previously and were accepted as evidence in favour of the solubility theory It was also found that the fibrogenic effects of certain silicates ran parallel with their solubilities 154 the weakness in this argument lies in the in- direct and unspecific association between the dust administered and the re- sulting fibrous growth except in the case of free silica The grounds for believing that silicic acid dissolved from particles of silica and silicate by the lung fluids is the agent which stimulates abnormal collagen production in connective tissue are extremely tenuous There is no positive evidence apart from the experiments of Kettle 25 139 by subcutaneous injection of colloidal silicic acid which must be regarded as doubtful because of the nature of his lesions these were not growing nodules but contained areas of scar tissue repairing regions of necrosis produced by the toxic action of colloidal silicic acid crystalline silica had a much smaller effect Necrosis in the silicotic nodule does not precede fibrosis but is sub- sequent to it ~* law Copyright U.S. by protected be may and party third a by Medicne of Library National the of colection the from copied - was page OE this NT on AN Con G.ra material 1s neran The - F DAVIES 340 of negative evidence is notably diminished when An apparent abundance the clinical reports of simple pneu- examined critically On the one hand are shadowing or reticula- with absence of nodulation diffuse ray to siliceous moconiosis and long histories of exposure tion without discrete opacities of the inhibition of solubility It is im- of the dusts These are cited as instances and analyses that accurate measurements of dust exposure in such cases perative be made before a pronouncement dust should be available and it is suggested that most of the cases These data are invariably lacking either of inert dust be accounted for in terms in this review can without tuberculosis in mentioned of diluted silica with or of the lungs or loading parenchyma each group work with animals Evidence of On the other hand is the experimental silica particles seems to the preventive action of a filmboyf Kierotntloexi2de5upuosning the method of subcu- solubility is definite rest upon a singleTehxepeefrfiemcetnotf aluminium oxide films on taneous injection dusts were pathogenic he sug- but King found that many low solubility dissolved away after the that this might be a result of the film being gested in the lungs 128 dust particles had deposited dust 150 is usually quoted as The work of Gardner on carborundum idea of mechanical trauma supporting the solubility ta hecoornyclaugsaiionnsttthhee aoultdhor himself maintained his by hard sharp particles of inhaled dust of silicon carbide upon guinea describing the effects of the control animals the lungs paper from He is discussing is worth quoting with others which had also inhaled pigs in comparison about which had inhaled dust the main mass of dust was scattered tubercle bacilli of low virulence and there was no fibrosis of the lung the air spaces in both the dust controls and the injected lymph nodes later date than did the cor- The tracheobronchial somewhat showed microscopic dust deposits at a found but it was series months an occasional particle was responding granite series at two considerable quantity of dust had collected not until the fourth month that any a steady increase in the deposits sixteenth month there was contained in all From then on until the five animals killed very large quantities were in both series In the last controls of this period there was a very definite parts of the nodes In the two dust obliterated the medullary sinuses This and somewhat extensive fibrosis which had of excessive amounts of reaction may be explained as the result of concentration irritant within a small focus the alteration of the course of the tuberculous Gardner also comments on low virulent organism from a self- induced by the inhalation of a tubercular process usually healing by resolution to a progressive limited process pneumonconiosis bronchopneumonia of tuberculosis and the initiation of fibrous Both the encouragement commonly accepted as specific attri- growth in the lymph nodes which are are here described butes of silica at least in experimental as the result of the presence of an inert dust THE 1 The difficulty of intravenous and intr the former techniqu quartz between 6 an particles between a stream to lungs live Necrosis and scar fo duced at the site of The idea that ad ad on account of its enl ments showed the e region of 1 to 2...15 The great objeci discovery that the s parallel with their f was established tha silicic acid could be effect even though forms of silica i.e. similar solubilities broadly increasing The experiment silicic acid and it of silica has been w ity theory of silicos both monomeric an ranging up to the c Molecularly dis _ or intravenous adm oral administration however are toxic fibrosis though no away 160 Polica similar to that pr prolific There has molecular silicic ac colloidal solution The immediate a nodule has ever animals while hun which acts like cr trations are abnor ferent from silicos These points a i.e. dry colloida tably diminished when reports of simple pneushadowing or reticula- f exposure to siliceous of solubility It is imre and analyses of the e made in such cases that most of the cases ms either of inert dust ithout tuberculosis in 1 animals Evidence of lica particles seems to the method of subcu- on solubility is definite e pathogenic he sug- ssolved away after the ) is usually quoted as of mechanical trauma mself maintained his 1 carbide upon guinea of the control animals which had also inhaled st was scattered about arenchyma arenchyma ontrols and the injected r date than did the corcle was found but it was y of dust had collected increase in the deposits ties were contained in all here was a very definite medullary sinuses This of excessive amounts of rse of the tuberculous organism from a self- rogressive tubercular : initiation of fibrous pted as specific attriis are here described THE PHYSICS AND CHEMISTRY OF DUST 341 The difficulty of carrying out inhalation experiments led to the use of intravenous and intratracheal injection Gardner & Cummings 151 using the former technique showed the importance of particle size Particles of quartz between 6 and 12...in size failed to produce silicotic nodules while particles between 1 and 3...did The particles were transported by the blood stream to lungs liver and spleen no reaction was observed in the kidneys Necrosis and scar formation resembling that described by Kettle was pro- duced at the site of injection in the ear The idea that a dust with a high specific surface was especially dangerous on account of its enhanced solubility was thus encouraged but later experi- ments showed the existence of an optimum particle size for fibrosis in the region of 1 to 2...152 153 The great objection to the solubility theory of silicosis came with the discovery that the solubilities of various forms of silica did not always run parallel with their pathological effects 149 154 155 In the first place it was established that samples of quartz from which an initial quantity of silicic acid could be leached readily did not thereby lose their fibrogenic effect even though their subsequent solubility was very low Secondly four forms of silica i.e. vitreous silica quartz cristobolite and tridymite have similar solubilities but produce differing fibrogenic effects the intensities broadly increasing in the order named 156 157 The experiments of Kettle were conducted with colloidal solutions of silicic acid and it is only recently that the physical chemistry of solutions of silica has been worked out sufficiently for their significance in the solubility theory of silicosis to be appreciated Solutions of silicic acid may contain both monomeric and dimeric molecules and polymerised aggregates of sizes ranging up to the colloidal particles present in Kettle's solutions Molecularly dispersed solutions are excreted to a large extent after oral or intravenous administration without damage to the animal 158 and after oral administration of silica and silicates in man 159 Colloidal solutions however are toxic 158 precipitate protein 160 and produce scar type fibrosis though not in the lung from which they are too rapidly drained away 160 Policard & Collet 161 claim that the fibrosis is qualitatively similar to that produced by crystalline quartz but quantitatively more prolific There has thus been a tendency to accept the innocuous nature of molecular silicic acid and to associate the growth of silicotic nodules with colloidal solution The immediate objection to this view is that nothing remotely resembling a nodule has ever been produced by the administration of colloidal silica to animals while human beings exposed to the dust of amorphous not vitreous which acts like crystalline silica rarely develop disease unless the concentrations are abnormally high in this case the clinical picture is quite dif- ferent from silicosis 81 to 84 These points are countered by arguing that inhaled dust of amorphous i.e. dry colloidal silica is so soluble that its action in lung tissue is pro- . law Copyright U.S. by protected protected be may and party third a by Medicne of Library National the of colection the from copied was page this on e Se material a The - ARENT, SN f= i) i i The material on this page was copied from the colection of the National Library of Medicne by a third party and may be protected by U.S. Copyright law 342 DAVIES a foundly modified whereas classical silicosis could be attributable to the of colloidal silicic acid in situ from particles of silica production the failure to find amor- Doubt is thrown upon the last hypothesis by silica in lung residues and by the fact that it is impossible to demon- phous of colloidal silicic acid in extracts from crystalline or strate the presence vitreous silica prepared under conditions which could hold in the lungs and temperatures colloidal solutions are formed di- rectAlty hbiugththpereqsusaunrteisty of silica dissolved has fallen to .02 per cent when the is down to 200 162 At body temperature solutions con- temperature taining less than .016 per cent SiO2 do not form colloid the transition from a true solution to a gel is slow in the vicinity of the above concentrations and it is extremely unlikely that so high a figure is ever attained in tissue fluids 163 Baumann 164 emphasised the complicated nature of solution equilib- rium between crystal colloid and molecular phase and the time taken to become stable as a result many determinations of alleged solubility were in reality measurements of rate of solution His figure for the solubility limit of molecular silicic acid was .012 to .014 cent over the pH range 4.5 to 9.0 with a much higher value in more per between amorphous alkaline media This figure was obtained for equilibrium silica and solution and it is interesting to note its closeness to the figures . above for crystals at 200 162 and gelling solutions prepared from sodium silicate 163 Paterson & Wheatley 165 found the equilibrium concentration of silicic acid to be .014 per cent irrespective of the presence of molecular in solutions made colloidal silica solution but could not obtain any colloid with crystalline silica feature of these investigations is the recurrence of a figure A suggestive crystalline and colloidal around .014 per cent for equilibrium with both material It is certainly possible that the crystal surface is contaminated locally or generally with colloidal particles which are attached too strongly to float away into the solution yet provide a reservoir for maintaining the molecular equilibrium concentration As far as silicosis is concerned the conclusion must be that any colloidal silica would have to be associated with the crystalline particles so closely as to necessitate their virtual contact with the forming cell in order to stimulate it The actual amount of colloid could be extremely small SUMMARY Pneumoconiosis is the term used for a group of lung diseases caused by the accumulation of dust in the lungs without systemic effects immediately attributable to the dust Some dusts are inert and produce neither an obvious reaction in the organ nor symptoms for diagnosis until a considerable quantity of dust has been collected Free silica usually in the form of quartz THE P causes silicosis in whic focal nodules which c There are many caused silicosis this is action of quartz by o crease the solubility o conclusive because t victim of a sufficient reach the lung alveol cause the classical sy . in experimental silic other hand there is is modified by the pr The production dusts of crystalline ... urally occurring the tuberculous infectio mentally by these d less focal The expei to produce such a re continued inhalation development of tu There are thus crystalline or vitre nodules in connecti developing collagen The pathology of a nature of the fibres of the primary lobu the ensuing fibrosis Colloidal silicic acid silicosis but the eff attributable to qua solution of quartz ttributable to the silica ilure to find amor- possible to demonrom crystalline or in the lungs ons are formed di! per cent when the cure solutions conthe transition from ve concentrations attained in tissue of solution equilib- the time taken to 1 solubility were in : acid was .012 to gher value in more etween amorphous ness to the figures . pared from sodium concentration of of the presence of in solutions made urrence of a figure lline and colloidal e is contaminated ached too strongly or maintaining the that any colloidal articles so closely ing cell in order to nely small diseases caused by ffects immediately neither an obvious til a considerable the form of quartz THE PHYSICS AND CHEMISTRY OF DUST 343 causes silicosis in which a continuous formation of collagen is stimulated in focal nodules which contain dust There are many reports of dusts containing quartz which have not caused silicosis this is commonly put down to the inhibition of the fibrogenic action of quartz by other constituents of the dust which are known to decrease the solubility of quartz Such reports however cannot be regarded as conclusive because there is seldom proof either of the inhalation by the victim of a sufficient concentration of quartz in particles fine enough to reach the lung alveoli or of the presence of enough quartz in the lungs to cause the classical symptoms of silicosis There is also a lack of parallelism in experimental silicosis between fibrogenic effect and solubility On the other hand there is some indication that the action of quartz in the lung is modified by the presence of a sufficient quantity of an inert diluent The production of developing fibrous growth in the lungs by inhaled dusts of crystalline or amorphous silicates is extremely doubtful As naturally occurring these dusts often contain free silica and the presence of tuberculous infection may simulate silicosis Fibrosis produced experimentally by these dusts is usually less than that produced by quartz and less focal The experimental techniques are drastic and might be expected to produce such a reaction more readily than would be the case with long continued inhalation Even inert dusts are suspected of encouraging the development of tuberculosis There are thus grounds for thinking that quartz and other forms of crystalline or vitreous silica are unique in causing proliferating fibrous nodules in connective tissue The only other dusts which cause rapidly developing collagenous growth are fibrous silicates loosely termed asbestos The pathology of asbestosis contrasts with silicosis because the physical nature of the fibres renders them liable to become caught in the fine airways of the primary lobule It is possible that chemical factors are concerned in the ensuing fibrosis which seems to lack the active progression of silicosis Colloidal silicic acid is a tissue poison and has been suspected as the cause of silicosis but the effects it produces lack characteristic features of the disease attributable to quartz dust and it is doubtful if it can be formed by the solution of quartz in the lungs law Copyright U.S. by protected be may and party third a by Medicne of Library National the of colection the from copied was page this on material The The material on this page was copied from the colection of the NationalNational Library of Medicine Medicine by a third party and may be protected by U.S. Copyright law 344 DAVIES LITERATURE CITED 1. 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Roche sociale 8 165-75 | 55. R^hrlW. Arb med 56. King E. J. Ray S. Med 7 37-41 19 57. Landwehr M. Atla und nutzbaren M Germany 286 pp 58. King E. J. Rogers G. J. Pathol Bac 59. Jones W. R. J. Hyg 60. Cooke W. E. J. Hy 61. Gerstel G. Arch Ge 62. Med Research Coun London England 63. Mavrogordato A. J 64. Lemon W. S. and 65. King E. J. Gilchrist 66. Landwehr M. Gl^...c 67. Weiland P. Arch ( 68. Hurlbut S. and Bey 69. Hass H. Zentr Geu 70. Dreessen W. C. Da and Trice M. F 1940 71. Govt India Ministr 72. Wade T. W. Mini Stationery Office ept 1953 ouncil Memo No. 25. Her ) , 119-150 October 1951 -26 1956 d Harding H. E. Lancet " 11 289 915 954 ' 10 512-21 1954 nd Occupational Med 10 2-20 1955 Assoc 127 701-5 1945 36-45 1948 rit J. Ind Med 13 9 23 teriol 139 314-24 1955 nd Med 8 62-67 68-73 1955 31-38 1949 , 91-99 1949 573-79 1949 H. Proc Roy Soc Med 2 grs and Inst Mining and G. Trans Inst Min- | ail et m^'dl^'gale8 81-84 | 56 J. 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