Document gybZ0L2mR44LyZDK6Mw2paXG

52 Twenty-first Congress--Satiana! Safety C nmtcil encounters incrraiing difficulty in farcing blood into the organs. In an attempt to c'OTTfiemate lire overu*<frked heart muscle becomes thicker and heavier and unless infection intervene* lire time eventually arrives when the heart tails and death occurs from this cause. The reasons far the prevalence of infection in the silicotic long arc not altogether clear. It is obvious tliat when the drainage system 1$ so obstructed by nodules of >ear tissue tliat more dust {articles can only be removed with difficulty, the same must lie true of liactma which may ! inlialcd. As a consequence they remain in the long and set up progressive infections. But this is not the whole story. The silicotic tissue apjarcnlly offers a jicculiarlv favorable soil tor the continued multiplication <>f tuljcrcie iacilli and jicrhaps other hacteria. Experiment has shown that even at tenuated organisms of this type will produce rapidly fatal tuberculosis in a silicotic guinea pig. Furthermore, inhaled silica dust will cause a pre-existing latent tulier- cuIou.n focus, harl*oring a feu* attenuated bacilli. to become progressive and spread. The cause of tin* effect tqion tulicrculous infection has not yet been ascertained iiut proliahfy ft is in some way associated with the death of tissue caused by the toxic silica. Associated with this factor is an increased activity of the phagocytes which are stimulated by the irritating silica so that these cells tend to migrate rapidly and carry tulierclc lacilti into jireviouslv unravolved portions of the long. .IshcsU's dust, perltaps liecaose of its filirous structure, is not transported very far within the lung. It tends to lodge along the walls oi the finer tube* and little of it is removed hv tin* Ivmpliatic drainage system. Tissue reaction, probably initiated by the *olmioti of the fillers, occurs m their immediate vicinity. As in the case of silica this reaction consists of an overgrowth of the connective tissues which is later transformed into leather-like scars. Aluminum oxide will serve admirably as an example of a non-siliceous dust wliose particles are as hard and ?harp as those oi crystalline silica. When a measured quantity oi such particles. 1 to 3 micra in diameter, are injected into tlic ear vein of a rahhh tin* majority of them come to rest in its liver and spleen. There they remain, apparently harmless, collected in large phagocytic cells and producing no reacti<i of tlie connective tissues for ai least two years. Injection of the same quantity of tlte same sized quartz panicles excites the formation of so much scar tissue tliat the functional elminus are almost completely destroyed and the organs are reduced to nodular masses of leather-like consistence. Carlmrunduni. the carbide of silicon, when inhaled by guinea {rigs for periods as lone as fain* years, likewise fails to excite significant overgrowth of the connective tissues. It produces only a low grade inflammatory change with no nodules. Instance-* such as those cited constitute the tasis for !cUcvinc that tlie cellular resjamse to dust {articles is not due to their lardness and sharjmess Iiut to chemical sulistances lilierated by tlte action of the tissues upon iltcm. The case for solubility Itas not been proven directly, for the detection of soluble silica in the tissues offers technical difficulties which today are insurmountable. Nevertheless this substance is known to lie a cell jniison and in weak concentrations h will provoke an overgrowth of the connective tissues. Mention should lie made of the effect of inhaled coal dust. Most city dwellers breathe in sufficient quantities of this material during an average life-time to pigment considerable areas of their lungs. Deposits of grey or black dust will be found along the course of the lymphatic drainage system hut this pigmentation is associated with little or no new growth of connective tissue. The coal miner's long is much blacker hut in most instances h also develops no deforming scars. When such reaction does occur analysis usually reveals appreciable amounts of silica in the lungs. The presence of excessive quantities of carlion dust apparently influences the localization of mod erate amounts of silica so that the latter is not dejiosrtcd tn nodules as m pure silicosis hut in streaks along lymph vessels as pure coal would localize. Coal miners' fibrosis, due to relatively small amounts of silica, is therenrre dif- Indttstrial Health Seetiov lerent from that of the pure quartz worker. When the amount of inlialtd silica is excessive, the effect of the coal is negligible and the reaction approximates that in pure silicosis. There is said to be more reaction to hard coal than to the bituminous variety but titere is evidence to suggest tint this is due to the greater amount of siliceous rock which must be worked in raining anthracite coal. Finally, consider the sDtcosis of granite cutters. This develops somcwliat more slowly than that of the pure quartz miner and it las been maintained tliat this is due to the relatively small amount of uncombmed silica m granite (25 to 40 per cent). Rut it is believed that other components of the glomerate granite may neutralize or at least inhibit the effects of the silica so that ouly after prolonged exposures to high concentrations does significant reaction occur. While typical silicotic nodules develop in guinea pigs inhaling pure quartz for a year, not even tlie earliest sug gestion of nodules have appeared in the lungs of animals inhaling comparable concen trations of granite (40 per cent silica) tor tour years. This brief discussion of some of the problems involved in pneumonokoniosis draws attention to the limitations of our present knowledge. It indicates that the reaction to an inhaled dust is determined by the chemical and proliably physical conqioshinn of that dust. It emphasizes the need to further study of different types of dust both in the pure state and in measured combinations. Tlic ultimate aim of such a study should be the neutralization of the toxic action of such dangerous substances as silica. ... * na-i. The Dust Content of the Atmosphere in Various Dusty Industries By J. J. BLOOMFIELD Sanitary Engineer, United States Pnblic Health Service. Washington, D. C. The speaker said in part: Tlie properties oi a given dost which determine its rapacity to produce pulmonary {athology are. tlie nature of the dust, tliat is. its chemical and mincralugical composition, its particle size, and finally the quantity of the dust dispersed m the atmosphere. Otic of the outstanding results of the last 20 years of research in the field of dust inhalation is the demonstration of the fact that, in general, the degree oi health hazards associated with the inhalation of any dust, all other factors re maining constant, is dependent tqwn the mineralogies! composition of the dust For example, it is imw well established that the initiation of certain types of dust, such as granite dust, will in time produce fibrosis of the lungs, at times associated with tuberculosis. In other cases exposure to dust nay result in the production of much less fibrosis without notable tendency toward subsequent tuberculosis; this is true of cement dust. And finally, there arc certain types of dust, as typified by marble dust, which in the quantities and lengths of exposure so far observed produce little lung fibrosis. In general, it has been found that those dusts which arc high in quartz content are the ones which produce a disabling fibrosis of the lungs most readily. So far as the size of the dust particle is concerned, it is apparent that in order for any given dust to produce injury to the lungs, it must gain access to the lorenchyma of the lung, the site where the harmful effects of the dust take place. It is known that not all of the particles of inhaled dust gain access or are retained by the human lung. In this connection it is of importance to have regard to the size of the dust particles present in the industrial atmosphere. With reference to the quantity of dust present in the air of a workroom h is apparent that when the dust concentration is high tlie exposed person will inhale a greater quantity in a given period of time than he will when the dust concentration of the atmosphere is relatively low. and since the rate of production of the fibrosis