Document DGwVpGjxyoVvEQ8RBNjByXqbd

FILE NAME: Saranac (SAR) DATE: 0000 DOC#: SAR010 DOCUMENT DESCRIPTION: Outline of Proposed Monograph on Asbestosis Saranac Lab Study under Grant from Asbestos Association *^4<S OUTLINE OF PROPOSED MONOGRAPH ON ASBESTOSIS Saranac Laboratory Study under Grant fron Asbestos Aecgglfttlon PART I HUMAN ASBESTOSIS 1 Human Pathology - a study of 28 autopsy cases^Illustrated 2 X-ray Patterns In Aabestosls, Illustrated 3 Ash and Mineral Values In Hunan Aabestosls 4 Complications of Aabestosls (a) Susceptibility to infection 1 Tuberculous 11 Non-Tuberculous 111 Cancer of the lung 5 Disability, causes end comparison with silicosis 6 Diagnosis . (a) (b) (c) (d) History of adequate exposure X-ray film pattern Physical examination Aabestosls bodies in sputum, their significance (2 ) PART II Experimental AwbgfltQda 1 Methods (a) Inhalation exposure to plant dusts. (b) Injeotlon Into lungs through trachea of pure minerals. (o ) Injection of pure minerals into other organs. 2 Species Susceptibility Man, guinea pigs, rabbits, cats, white nice and rats, dogs. 3 Peculiar Characteristics of Asbes.tosis (a) Unusual locallzaion of chrysotile fibre in lungs. (b) Rate of resultant tissue reaction nore rapid than to quartz. (c) Reaction to chrysotile not progressive after exposure ceases; again the reverse of the situation in silicosis. (d) AsbestOBis Bodies 1 Conpoaltion and methods of formation, ii Occurence in different species, ill Formation does not parallel development of fibrosis, lv Gradual disappearance after exposure ceases. 4 Comparative Effects of Different Asbestlform minerals. (a) Canadian Chrysotile. (b) Arizona Chrysotile, low iron. (c) Crooldollte 1 Bolivian specimen, stiff and elastic, ii South African, soft and flexible. (d) Anthophyllite (e) Amoslte. (f) Tremolite. 5 Effects of Control Minerals (a) Orannular Serpentine, same ohenical composition as chrysotile. (b) Glass Wool, a synthetic silicate fibre. (c) Bruoite, a fibrous magnesium hydroxide almost free of silica 6 Chemical Composition of Asbestlform minerals in Relation to Irritation. (a) Nothing in composition correlated with relative lrritatin capacity. (b) Preliminary acid treatment 1 Hydrochloric aoid 11 Carbonic acid 4 (3 ) (c) Effects of Aluminum 7 Physical Properties in Relation to Irritation !a) b) Length Effeot of of fibre Crushing o) Heat treatment 8 Nature and Significance of Aabestosia Body (a) Formation (b) Protective effeot preventing further irritation (o) Ultimate solubility in tissue 9 Theories of Action of Aabeatiforn Minerals (a) Chemical - reasons for considering invalid (b) Mechanical - experimental demonstration of. 10 Complications (a) Infection, tuberculosis and other varieties (b) Cancer of lung - experimental data suggestive but not proven 11 Disability 12 Essential Features of Hazardous Exposure (a) Nature of dust - fibrous component and size factors (b) Atmospheric Concentrations - probably lower than for quartz 1 Inadequacy of standard impinger sampling method which does not oollect the dangerous fibres il Electrostatic preclpitatar'eampling preferable but W method must be modified (c)'Duration of Exposure 13 Recommendations for a New Standard of Safe Atmospheric Con centrations of Asbestos Dust (a) The Quasi-official standard-of 4 to 5 million particles per cu. ft. (b) Work upon better method of sampling (c) Necessity for comparison of results with X-ray findings in employees 14 Prevention (a) Chemical means not practical (4) 1 Aci&osia necessary to dissolve fibre in lungs worse than Asbe8toeis 11 A1uninun Therapy lnapplioable iii Chief reliance still upon dust prevention with speoial enphasls upon the fibrous oonponents \ -I- -A-SB-E-5-T-0-S-IS - -A-NU-C-T-E-D --OU^-TL-I-N-E--I-N-D-I-CA-T-I-N-G--R-E-SU-L-T-S PJHT I - HUMAN ASBE3T03I3 1 Huiaan Pathology and. X-ray Patterns - Desorlptlon Based upon 23 human autopsies 2 Aah and Mineral Values In Hunan Lungs. 3 Complication of Asbestosis (a) Susceptibility to Infection 1 Tuberculous- High incidence In English experience not duplicated in surveys of American Plants. Available autopsy statistics deceiving because of sel ection of material. ii Non-Tuberoulousu The sane reason probably applies should be checked, by analysis of absenteeisn anong asbestos workers. iii Cancer of Lung Ditto, but there are now on record 10 caaes of. lung cancer in asbestos workers. Compared to the total number of autopsies on asbeBtosia, this incidence is excessive. No Buch frequency has been discovered in silicosis ,^r other forms of pneumoconio sis exceptA the Sohneeberg mines of radio active ores. The evidence is 'suggestive but not conclusive that asbestosis may precipitate the development of oancer in susceptible individuals. 4 Disability Clinical experience suggests that truly disabling asbestosis Is manifested by less striking X-ray changes than a corresponding de-ree of silicosis. Such disability in asbestosis is due to disease within the lungs and not to secondary heart disease. As in sillco81s , associated pulmonary infection increases the amount severity of the dust fibrosis with resultant accentuation of disability. There is urgent need for a' careful physiological study of pulmonary function in asbestosis of varying severity. Undoubtedly, there are many diagnosable cases with no significant disability. 5 Diacr.osis depends upon three factors. (a) History of adequate exposure, usually 6 to S years, some times longer, at work where both the concentration and character of the "asbestos" dust are hazardous. 0 ^ ^ t-0 **-: r w r / v f f t ? * *"* <*C-' --* *< 4 . rrt- * ,l ' * . I . ' ' t;. (b) Evidence of diseaseiin a characteristic X-ray patt ern. - : Is -V-. (c) A physical jxanlnation which. reveals certain characteristics- signs and nay reveal evidences of disability if present..^-' (d) Asbestoais bodieo in'the eputun are confirmatory when the-'', previous.factors are'all positive. However, the bodies nay be absent,-' particularly in the absence of bronchitis .-V;;- infection. Asbestosobodies unsupported by other evidence do not make .a diagnosis. 'Occasional ones have been found in about 15 autopsy specinens of persons with no known exposure and r.o fibrosis, probably 'of :non-ocoupational origin. . 'T' 1.i' PART II Experimental Aabestoslg I .Hethoda 't (a) Inhalation Exposures .to Plant Du3jC .-.Specific fibrosis .in"h lungs, but no.ohangea elsewhere. S' .. - IV - ' ./ : ' -. (b) Injections of -Suspension^ of Pure Minerals into Traohea r~ .b:'" Similar results. **-*. '*.. r v ,** ,*0 j . q . v . ',-vrr^H *-p.\ (c) Injection of Suspensions of Pure'Mineral Into other organs - . Fibres dissolved; no asbestosia b o d i e s t i s s u e reaction^con fined to phygocytosia and encapsulation. Compare'the asbestos c& sraa of human, subjects ;. .'i .. j */ \ ** * *. **'"' N-*-* * '\\ SI II 37;clt8 SuscenU M l l u U - Species Unlike free allioa,.asbestos-'does not^prbduoe lts.epeoifio effec .in any organ of- any: speoies.-of,'anihair-i.;'`IV.'.oau8efl fibrosio :only- the lungs of man and those-fof'a.'few-'of.-.the.species-tested, v.^.'f-h - . i r s - '> - -- 1N.'*i f . t \ '. .4 * . i . f- 9 r - 2 / , * ... .'/ ?*.. * **_ t ;.* ' , * \ i t f Fibrosis A s b e s t o s ' B o d i e s Soeolea-* Fibrosla Aebeatos-Bo Man 4+ Guinea Pig 24 Rabbit 4+ A ':- 3+' h * -vh'-.- C a r - > . - VhitaAHouse '0 Whito Rat -O'"0 P i.' Ill smalT Atypical asbestos bodleal:^-- . Peculiar Characteristics of A s b e a t o n i q \,i ,, - , -.J.'f -W -Vo'rV- 1 Fibres like ohrysotlle having- a oertain degree of flexibility and elasticity accumulate within the finest air tubes; granular dust la oarried further on and la widely scattered through the terminal air spaces. (b) Rate of tissue reaotlon to asbestos la much more rapid than to an active dust like quartz. Evidences of formation appear as soon as sufficient concentration of fibres has localized 'in speolfio areas; with quartz, there is a latent period of months. (c) Reaction to asbestos does not progress on cessation of expos ure. Young scar tissue that may have formed, contracts and becomes more dense but the area of involvement decreases insize. In sllioosis, the -young nodules become larger after exposure ceases. (d) Aabestosis Bodies are a specific concommitant of this form of pneumoconiosis. They are due to a deposit of protein and iron upon the surface of Inhaled fibres. In guinea pigs they form after about 60 days of contaot with the tissue. They are abund ant in man and guinea pigs, (See paragraph 2 above) but much larger in the former probably because the larger sized air tube admit larger fibres. In cats,- rabbits and mice, there is an atypical coating of a few of the fibres after muoh longer resi dence in the lungs; in rats and dogs no bodies could be dis covered. From paragraph 2 it is apparent that their occurence does not parallel development of fl'oroels. In lung injection experiment!, the bodies have u s t developed after fibrosis p.dvr.nced. The number of bodies seems to decrease several years after exposure oeases. Conoe,rp.Uye Sffacts Different Agbeatosls Minerals * - (a) Canadian ^hrvsotlle - highly irritating. (b) Arizona ^hrysotlle (low in Iron) equally Irritating and pro duces Just.-as many aabestosis bodies as the Canadian product with over 11 times as much iron. (c) Crocldolite - The South African blue asbestos is known to cause asbestoais. Only a limited supply of this material in pure form was available, most of it was used'earlier in the work in non-productive experiments. For the later critical injection tests into the lungs, a Bolivian variety was substituted be cause of its high purity. Its fibres were much atralghter, atlffer and more elastic than the cottony South African variety. Perhaps because of these peculiarities, it has not given reactions comparable to ohrysotlle. It produced asbeBtosis bodies but did not localize in the terminal air tubes nor cause any fibrosis. Tests now being repeated with a typical South African crocldolite with physical characteristics simulating ohrysotlle. 4- (d) AnthoohyXllte -'stiff, straight fibres - atypical asbeBtosia bodies forns slowly but no localization or fibrosis in lungs. (e) Amoalte - Ditto. .yf (f) Anohlbole - Ditto. . i .\ '/ (?) Trenollte - Ditto but very few asbestosis bodiea - Observation being oontlnued. . ,, `.` >- V Control Mineral . '*V* ,, (a) Granular Serpentine of same chemioal composition aa chrycotlle is inert causing no fibrosis in lungs or other organs. Ut V; attraots iron from the lungs but of oourae, no "bodies11 develop. (b) Glass ^ o o l (a synthetic silicate) fibres are not inhalabla from air-borns suspensions, apparently because of their stiffnese (the diameter is not responsible as some used were less than'."-'? 1 micron thick) On injeotlon into the lungs, they do not >r ' localize in the air .tubes but are widely scattered. They cause ' no fibrosis. After 3 or 4 months in contact with lung fluid,- V a few glass fibres take up iron but remain smooth. They never shew the swollen ends and lateral projections of the true asbestosis bodies. (c) Bruclte of interest because it la a fibrous mineral praotically free of silica (o.9). Crystallographlcally the arrangement of its $ g ar*<d OH groups in each unit oell is similar to that in chrysotile. The sample used also contained about 16^ iron, pro bably from contaminating magnetite. The fibres are stiff and needle like. Observ&ions not yet completed but after 2 months in the lungs, typipal asbestosis bodies develop but there la ae yet no fibrosis, ^'he fibre are scattered .through the lung instead of being.localized inside the terminal air tubes and tissue reaction"..pccur8 around, instead of within the tubes. VI Chemical Composition in Kglatlon to Irritation (a) Kotrhing in the following chemical compositions can be cor related with variations in capacity to provoke tissue reaction. (See Table Next .Page) V . i fur Chrys- Crooid- ,[ P-3___ P * 1 , 0 5 ..P* 0 z.zii 0 M . 99* -16.27* 4,29* AlsCh ___ 0 . 3 6 * 1.02* Co. 0 0.05* 0.79* 0 3 8 .7 7 * ... 1 2 ,2 5 * K<vo_ 0 0 6,92 . 0.08 0.57 Lo.ss 4.105'0 4 . 3 0 0.0 2 ' >105 14.92 2.55 :;4 6 l 2 3 * "' 6 6 . 2 0 * ' o . s o * < `^ !' 0. . 5 1$ 0 ? ^ .4,06* ' '`3 . 60? l' " 7 , 2 1 * - 6 , 7 8 * 33.8 3 * 0 0 j "* '9 . 35* ' ' Q.25* 1.09* . 1*69* 0,56* 0.46* V- .....0 , 4 4 * 29.54* 2.01* 6.29* 12.22*. 23.29* *' 4 . 4 5 * 0 , 4 0 * ' r'""`v ' 20 ,*52*' 5 3,99* 0.52 0.33 0.40 6,7 8 -".0.91 . 0,15 0.10 0 , 1 2 " 0 , 9 9 ' OflS '1' '* .. 0 , 0 2 0.66 0,32 - 0,34 . 0.53 2.42 1.51 3 , 5 9 ''"' 2 . 7 8 ' 26.6 6 *' . . V - . ( . . s , . , V .1 (b) Acid treatment,of ohryootile fibrso ^ _ Jr. : y ~v. .' ... ' yX~ 1 One hour in dilute or concentrated'HCL does not alter~ap-*--- pearanoe of fibre but after suoh treatment it rapidly'dia- solves and disappears on injecting into living tissues; ii Treatnent with CO2 bubbled through water or lung Juice suspensions of chrysotile fibreswcauaes partial solution with liberation of silica and magnesia. (c) Colloidal allunina does not neutralize the "offects of asbestos as it does quartz. Op injecting ohrysotile suspended in aluminum hydrate solution, fibrosis and asbestos bodies dev elop at the usual rate. It remains to demonstrate whether the fibreB'beoome ooated with a layer of aluminum monohydrate as . has been proved in the case of quartz. If thsy have, the coati does not affeot their oapaoity to irritate tissue. , VII Physical Properties In Relation to Irritation of Lung Tissue (a) Length of Fibre Short chrysotile fibres under 3 miorons are practically inert. 20 to 50 micron fibres cause typical fibrosis. The effects of longer ones could not be tested for technical reasons. (b) Crushing completely destroys the fibrous structure of chrysotile. With loss of structure, all. oapacity to irritate disappears. , ;- \ \\Xb (3 b ribre*3truoturo'lo preserved.'-;.`Fibres become' extrehs>l:r brittle^ '"The physical ohange altera typical looalitat 1on~within ' t h e .lungs, no flbroaie develops ,-reaation-Hmitod to .`phyagocytoeiaV-r'- ! No asbestoaia bodies' formed. ; y %*'<?'''** -i>' ^Tr-; VIII Nature and Sjgnlf loanee'of Aabcetoela B odlen ,, ... . ' (a) Bodies, probably result from dopoaltionTof Iron'-.ana organic natter on a slowly..dlooolvlng-fibre .oflasbeatoqVp-rThe souroe .. of the iron is more likely to;bai.tho lung tissue .than'the mineral itcelf aa tho coating "In'-Just 'as-heavy-on -fibrous ^ minerals of lew iron -contontp-aa' .upon, thooe `high.in' iron, (b) The effect of aabeotoois' bodylfornation'lo ascumod to be pro-;r tective althoughit has not 'been .poaaiblaito^ ieolato a large . enough quantity of. theae structures /in .unaltorcd'.fora for , purposes of teat. The smooth'rounded-end3.~ presented-by the bodies would not 'be meohanloalJ^.l. l r r l t a t d a g ' (c) If they were oapabla of causing-irritation,'xtho ^fibrosis in the lungs should progress after exposure.ceases.which it does not. (d) The gradual disappearance of bodies (and'^fibres) long after ' exposure'^oints. to ultimate solubility in* tissue fluids. (e) ^he bodies are probably a fortuitous oonoocnitant rather than' " a cause of fibrosis. IX Theories of Irritant Action of Aebestifora Mlnerfrla (a) Chemical These experiments do not confirm the theory that asbestoais is merely a form of oilicosis resulting from free silica liberated in the solution of a silicate moleoule. If this were true asbestos,like auartz^^hould cause fibrosis in any organ of any species for the experiments have shown that injected asbestos dissolves in these looatlons. However, it Ices not. c*u3e such reaction In any location but the lungs of * `' species. (b) Mechanical Irritation We are proposing the theory of mechanical irritation which is manifested only in the lungs because this organ is the only one whose normal physiological functions involve a high degree of mobility. Experiments designed to prove the necessity for notion in this tissue have failed for technical reasons. For this theory to be applicable,it la necessary that the fibres be concentrated in the fb7 e terminal air tubes. It has be^rv.shown that only ohrysotlle of the asbeatiform minerals thus farinas the proper physical characteristics.to insure such localization, it la also essential that'the fibre shall persist long enough before it dissolves in the;lungs of epsciee like nice, rats,+ dogs. It apparently dlosoivea so rapidly that it exerts no irritation. Similarly rapid.eolutlon may explain in part, the lack of fibrosis in organa other than the lungs. \ b lr(_ (q) -7- The fibres oust be long enough so that they cannot be completely !' surrounded by_phagocytic cells which'would prevent contact of these round, broken'ends with the delioate cells supporting the air tubes. Observation has demonstrated that these conditions are realized in guinea pigs treated with long fibre chrysotile and fibrosis results. With the other asbestiform minerals that have been tested, some or all of the prerequisite were lacking and no fibrosis developed. (c) If the irritation were chemical, fine serpentine which has the sane* chemical composition as chrysotile should have also caused fibrosis. The crushed chrysotile shoudl have been more active than intact fibres, because of the greater surface areas ex posed to body fluids. On the assumption that chrysotile, like ouart z , becomes coated with a very thin layer of aluminas on treatment with colloidal aluminum hydroxide, capacity .to cause fibrosis should be destroyed if the aotipn were chemical but such 15 not the case. (d) 1'he heavy coating resulting from asoestosis body formation ap parently does stop tissue reaction but here the effects are probably mechanical for reasons cited. (e) Heat sufficient to alter chemical strue fare d estroys power to Irritate but it also altera essential physical characteristic that affect localization of the fibres in the lungs. X Complications (a) Susceptibility to Infection d i/ih i Tuberculous - Asbestos behaves like most other mineral^ in this respect and not like ouartz which specifically increases native susceptibility to the tubercle bacillus. This in fection may spread for a time but then heals. The resultant fibrosis accentuates that oaused by the mineral fibre. 11 Mon-Tuberculous - of no greater frequency than in animala inhaling dusts of other kinds. Occasional epidemics of pneumonia occur in our dust rooms, but these are due to methods of housing rather than to dust; they o ttn also occur in unexposed animals. lll'v Cancer of Lunro No experiments wereAdeslgned to elucidate this point but certain evidence suggests that aabestoeis nay actually favor development of tumors in susceptible species. 1 In guinea pigs, rabbits/ rata, oats and dogs lung tumors are rare. 2 When these apeoiea were subjected to 2 to 3 years in halation of asbestos dust, the incidence of lung tumor was not increased. 3 Some strains of white nioe do develop tumors without apparent cause. j 4 auch a strain of white nice was unintentionally UBed in three inhalation experiments with asbestos. 5 Of 11 nice inhaling long fibre asbestos for 15 to 24 norths 8 developed nallgnant tunora in their lungs and 6 of then . had tunora in other organs. The incidence rate jll.M la excessive. 6 Of 22 nice inhaling short fibre asbestos for not longer than 12 nonths only 3 developed lung tunora. Rate 13.6% 7 As oontrols, we have only the experience with nioe in other' dust experiments. -- ^or short periods. there were 51 nice exposed to 4 other hinds of dust for 10 to 12 nonths. Incidence of lung tumor 1.9*. For lonr periods. there were 143 nice exposed to 4 different kinds of dust, including pure quartz, 23 to 31 nonths. For all this group of nice the average incidence of lung tunor was 13.8*: the highest rate (25*) was in a subgroup exposed to flint dust. Thus the incidence of lung cancer in the long fibre asbestos nioe was over 15 tines the average for nice inhaling other dusts for comparable periods and over 3 tines the maxinun for any other'group. Mice exposed to the practioally Inert short fibre asbestos showed fewer lung tumors although 7 times mor8 than thoae in short exposureo to other dusts. ^'hese observations are suggestive but not conclusive evidence of a cancer stimulating aotion by asbestos dust. They are open to several oriticisms. The strain of nice was not the same in the asbestos experiment as in many of the others olted; apparently the former were unusually susceptible. Not enough anlnala survived in the dust for longer thgn the 15 months apparently necessary to produce many-tuners. ihere were no unexposed oontrols of the same strain and age end no dlmilar controls exposed to other dusts. It is hoped that this experiment can be repeated under properly controlled conditions to determine whether asbestos actually favors cancer.of the lung. XI Disability Cannot be determined in animals, ^he accidental deaths were from the same causes net with in all our dust inhalation experi ments. \ XII ***' /,- p .V. t.** ..-Vf^T.Ti*- (a) Nature of Puei if- r*.--*.;.' ` ^ .. - " -J * tt* & * fr 1 *he hazrda increases with the proportion of ..intact fibres r^;-. in the dust. Granular material and crushed fibre are ^11? inert diluents. '**v r.y': A` >!>> ii ^he long fibres must be thin enough (1-3 Microns) and short :\J ; enough (under 50 Microns?) to be inhaled. ill Very short fibres (under 3 Microns) are practically inert. (b) Atno80herlc Concentration Still under study. Apparently this factor is lower than in the case of dusts oonposed of granular minerals but methods of estimation are misleading. i ' i The average standard Public ^salth Service inplnger count in the long fibre asbestos dust room'was 40 million particles per cu. ft. of air. *hia' concentration;caused fibrosis visible to the naXed eye in 20 to 24 months. For comparison the average inplnger oounta in an experiment with pure quartz was 120 million particles per cu . 'ft.*and fibrosiB developed at about the same rate. ii However, inplnger oounta are deceptive because by thia method of sampling very few fibres, which are the significant elements in the dust are o o l l e o t e d . v ' : ill Sampling with an electrostatic precipitator is a much more efficient means of collecting fibres from air-borne sus pensions. 8amples from our long fibre asbestos room showed that the dust in the air contained 32.5,3 of fibres few of which had been oolleoted or counted in the inplnger sample. The latter sampled largely the inert granular parti- oles. . _ ' lv As ordinarily employed precipitator samples are weighed and the results expressed in mg. per cublo foot of air. There is no means of converting such values into numbers of ^particles particularly when these vary in size, shape and `specific gravity. -*I.1 .,y ' n* . v Simultaneous sampling with precipitator and standard in plnger yielded the respective values of 0.65 mg and 60 mil lion particles per cubic foot of air. vi *heoretioally the best Index of hazard would be either the number or weight of fibrous elements in the dust. i is> (s (3) -10- (c ) Duration of Exposure V4-?A.,: - i Fibrosis visible to the naked eye after 13 nontha exposure,' increases in extent in subsequent 13 .nontha. * , ' rr' 11 The span of U f a of our noet susceptible laboratory animal,/, the.guinea pi has prevented continuing`exposure longer than three years. In this period only'the comparatively early / ;. ' ,, ` t: -j>, stagep of'asbestosie have.been-produced.r With the knowledge that we have gained, it- Is- probable that more extensive disease could have been produced with a purer long fibre chrysotile. The long lived species,-like cats, dogs are un i" &*. Mnz I fortunately not susceptible-'.. :iil . For these reasons X-ray changes have been nininal and we were not able to fulfill one of the objectives of this pro- " ' gram. , > , Recommendation f o r 'a New Standard of S a f e 'Atmospheric Concentration of.Asbestos .gust. ^ /> T< :: few * - Pjr'.>.' (a) While there is no official standard, the'tentative one of V .' 4 or million particles per cubic foot.-of air is frequently cuoted. !f.V < (b) This is probably unreliable because it ;is`based upon sampling, f*. I*V1' ,'. L*'. with a standard iapinger which we have?shown does not collect n e a r of the fibres that are the source of_.hp.zard. (c) We now think that a standard should be'baaed upon samples collected with an electrostatic precipitator If it is feasible to determine readily the relative proportion of-fibres ir. such material. v U) Work is still in progress upon-the lAttejr-poipt. (e) To be of -value the* new standard would.''h.a'Yehto-:be correlsated with- thev'X-rpy findings 'upon'`employee a/expo Bed.:to .differ ent concentrations of duat. i.'i * ' . . ji. *rf >vN.*v\y\t ,'vv * :. />% XIV Frever.tic n of Asbestos!iid -" The experiments have failed .to^aevelop .any^practical 'chemical ^ j ^ j ,, * a . . * ________ _____ ______________-_<s*?t_-__'___**__ _ a . ' j "> , _ . :f: ' :sp means of neutralizing the action'of fibrous-asbestos - t". c [a) To alter the :hunan?lung so' that it vouldTdi'a'30lve7asbestOE fibres rapidly like a rat would necessitate.'(yrobabl-y) creating an acidosis whioh would be ytforse ^than the effect* the fibrosis. - > :" /.. l ' ' v. ' . . 4 ' .Vi >` *V, - ' . >&:'<?& -V-. ' ... ^ ... rI (b)'. Apparently alunlnur* .T '.has .little lnflilenda-' '" -y '* ' <* .(o)`;Hovever, It wpvld; great.'rtheoretlcal^nterest'to treatttl&Sr*. sV <& . few oesea vith.'roart'Ajspnoea'liroo aob?ato8lB;.by`.alunlnua';inf^^:.