Document 2RzxJZpy3gnGYQ3dEGkb14bGa

ST0 0 I ! f, | o -1") / >38 A ' j - .:v . j~ *.'ec _ a$soc dr Experimental Asbestosis Studies on the Progressiveness of the Pulmonary Fibrosis Caused by Chrysolite Dost f*aui ('Tro##. MD. and Robert T P de Trettil*. Pittsburgh f .-V \ fO T HE unreliability of symptoms as a crite rion for the progression of pulmonary fibro sis was underlined in a medical and psychi atric study of coal miners with respiratory complaints. Here, a very significant associa tion was observed between a recognizable p6ychoneurotic factor and an apparent worsening of the clinical condition: of 40 patients studied, only 12.5% had disability on "physical" grounds alone; 35% had dis ability on psychiatric grounds alone; and the remainder on both.1 Furthermore, discerning clinicians recog nize that opinions concerning the progres sion of a pulmonary fibrosis based upon the symptomatology (eg. shortness of breath) and a roentgenologic evaluation, even when reenforced by lung function studies may be quite erroneous. In the presence of a superadded coincidental pulmonary illness, such signs and symptoms may be reversible in whole or in part between such episodes, which include covert and overt acute pneumonitides, pulmonary edema, and allergic or chronic bronchitis--with or without em physema, or emphysema without bronchitis. Such diagnostic difficulties were the subject of a recent symposium on emphysema in :nd ustry. As uncertain as are the clinical criteria of progression of pneumoconiosis, very little help has come from postmortem studies of human lungs or those of experimental ani mals in defining the criteria by which progression at pneumoconiosis may be de- Sufoonttad (or publication Aug 9, 1966: accepted Aug 15. From the Industrial Hygiene Foundation. Mellon Institute. Pittsburgh. Read before the Hatch Symposium, Graduate School of Public Health. University of Pittsburgh, Julv 18-19. 1966. Reprint requests to the Industrial Health Founda tion. Mellon Institute. 4400 Fifth Ave. Pittsburgh 15219 (Dr. Gross). termined. This is- particularly true of asbes tosis. It is the purpose of this paper to define some of the anatomic itfeQBttfcd# pgpgreusion of aabeetoei^nd, to ittfinninfc^gfagther or not asbestosis caused by cmyaotue dust u progressive. Methods and Materials Lung burdens of chryvotito asbestos dust were imposed upon rats, hamstoa, and guinea pigs by exposure,iajphalatitg chgafasa as well as by intra^w4wsMpjgcna^ Most of the ani mals exposecTTo'chisi in an mhalstiou <*--! and reported in this study were part of a larger investigation that will be reported separately. The inhalation chamber in which aD animals (except four guinea pigs) wut exposed to dust, measured 8x8x8 fast. The animals were housed in wire cages that were suspended In racks. Periodically, these sugea wet* rotated so that inequalities in dust Mpoame caused by po sition were largely obvtutod. lb* exposures were for six boors par dap. five days par wash. The total exposure varied, as listed in the table. The chrysotile adbaetoa was bnUmilled and then led into a heomiaiawU (anfified bans a design by Holt and Young*). Thai sa* fuwridad with inlet and outlet tidteg so aeiangad that the comminuted asbastna was fad hack cadbnafly into the haimnerauB. At the same tone, tha ultrafines were allowed to waft upward into the inhalation chamber. Two sf thus hammenaills provided the chamber wfifc suSdaut-dnat to av erage M mg/cu m with u rang! el 42 mg/cu m to 146 mg/cu m. Hm aebeatoe dual cloud was evaluated by sampling with a ha stags das se lective dsvtoe. stmfiar to Assign to Oat pro posed by Wilgb* and apeiatod at 90 li tera/minuto lbs first stage <d tbs toatniiaanl was a Iririswilal elutriates witii selector churacteristici saonmmended by tbs Jnhannaalsmg Tnnininmidnus Conferva* of 1969, it 't acceptance sf aH particles bgriggJmtoi Mb tllng velocities greater than |f--* sphetd H Ifthty I gm/vu at, 90% arrantouns Arch Emtron Health--Vol 15. Nov 1997 DOW-1454 jf parades, the terminal settling itiocnv < f which is equivalent to 3u spherical parades 1 gm/cu cm density. and dropping to z. ro ac ceptance of particle* having terminal settling velocities equal to a lu sphere of 1 gm/cu cm density. All particles penetrating the first stage elutriator were cnn-ii/iered "respirable" ana were collected on a permeable-membrane filter which acted as the instrument's second stage The filter was dried and weighed prior to and after collection of the sample In this man ner. it was found that 63% to 79% of the sus pended asbestos dust in the exposure chamher was respirable, ie, it* terminal settling velocity was less than that of a 7 1 sphere of 1 gm/cu cm density. The exhaust air from the inhalation chamber was drawn by suction through a pair of elec trostatic precipitators. The chamber air was consequently always under negative pressure as long as the ham memulls were operating. When the hammermills were shut down, fresh air was pulled through the chamber before the door was opened. Periodically, dust from the electrostatic pre cipitators was collected and weighed. Since a record of the air flow through the chamber was kept, it was possible to calculate the average dust concentration in the chamber air by divid ing the weight of the dust collected within a time period bv the volume of air flowing through the chamber within that time. As seen in the table, four guinea pigs were exposed to a concentration of chrysotile dust sveraging about 20 mg/cu m. For this exposure, a smaller chamber waa used and the dust was prepared by atomizing a suspension of ballmilled chrysotile asbestos at a pressure of 100 Ib/sq in and impinging the emergent jet a near- sonic velocity against a tool steel baffle. The av erage fiber length of this dust was 0 92n as de termined bv measurements from electron pho tomicrographs. Inasmuch as other data on the size distribution of the dust are not available, it is not possible to state what percentage of the dust suspended in the chamber air was respi ra ble. These animals were exposed for three months to this dust. or lptratracheal injections, the dust collect ed from the electrostatic precipitators was sus pended in water so that l ml contained 3.5 mg 'hjst. The rats and hamsters were injected intratracheally, some repeatedly, as listed in the table. The injections were made under light ether anesthesia with the aid of an illuminated speculum that allowed visualization of the vo cal chorda. Some animals died at various times following the imposition of the dust burden. Others were killed approximately two years after the impost - Ammtlt Ei potid to. or Injected Intratrochoulty With, ChtytoVla Aibartoi Quit 1 nhaletion Exposure (Months) t Dust tntra T.ma Concentration (rachaai En<a of Species (average) inaction Eiposure No. (86 mg/ (20 mg/ No 3.5 mg to Oatn Ammon cu m) cu m) Mictions iMontns) Rats - 2 0 25 6 05 61 62 A4 48 5l 52 44 10 6 52 Mama!*?* i; 1i 13 2* 5 l l 25 24 l 1 2* 23 0 6 21 3.5 1 7 21 21 21 21 91 52 14 Qulau Rift 6 0.5-5.5 43 10 )3.5-2 1 12.5 16.5 0 04 tion of the lung dust burden as shown in the table. All animals were sutopsied, the lungs were removed and expanded with 4% formaldehyde solution under a pressure of 12 cm water. Paraffin sections were cut at 6*. Cleared un stained sections were examined under dark- field conditions4 and appropriate fields were photographed on 35 mm film. These sections were then stained with hematoxylin and eoain and the same fields repbotographed. After de- i-oloriration and silver impregnation (Gordon and Sweets), the field# were photographed for the third time. A fourth photograph at the same fields was after the sections hasl been subjected to microiacineratioB at 600 C for an hour and treated frith concentrated hy drochloric acid after cooling. Representative lesions in the lungs of control animals were also photographed for jairpoees of comparison with the experimental lessons. There were 16 rata, 29 hamsters, and 13 guinea pigs that had been part of the shipments at the animals later put on test, but had been set aside away from the dust exposure as laborato ry controls. The results at this investigation are baaed largely upon a comparative stndy of about 700 fields selected from the sections of 76 animals. Results Rata (Intratracheal Injection).--Itnmedi- Arch Environ Health--Vol la, Sov 1967 ' r. cr 640 EXPERIMENTAL ASBESTUSIS--MROSS <ft DE TREVILLE 2 l'Ji I 00IS Fig 1.--Ash pattern of acid-insoluble mstsnal In lung of rat ImmaOlately following Intratracheal Injec tion of chrysotlle dust Alveolar ducts ara outlined by fairly thick, continuous coating of dust Some dust, mostly In the form of discontinuous deposits. Is also `ound In some distal alveoli. Section wes sublectad to microtncineratlon followed by treatment with concen trated hydrochloric acid (X 1501. ately after the intratracheal injection of chrysotile, the dust was seen applied as a uniform and continuous, dense coating upon the respiratory surfaces of the alveolar ducts and their evaginating alveoli (Fig 1). The lumens were everywhere widely patent. Sur face coating by the dust of some of the distal alveoli was also observed, but not regularly. After 72 hours, the proximal portion of the racemus3 was a nearly solid, cellular structure in which the lumens of the respira tory bronchiole and alveolar ducts were oblit erated by a polypoid mass of ovoid and plump spindle-shaped cells which also oblit erated the lumens of the evaginating al veoli. A highly significant change in the distribution of the asbestos dust was now Fig 2.--Ash pattern of scld-kwofufafo material tttrsa days aftar Intritrachaat tnJsoUaw of ctvyaeMa dual In rat. Oust now In tha form of Socmlant maaaaa of ipfculated sggrsgslai. team* to farm casts of eJvaofar ducts and nils tfwlr lumens. Vary uttto dust Is noted In tha parlpharsl alveoli (X 150). observed. The dust permeated the ooduaive inflammatory tiame and thereby formed a cast of what was once the lumen (Fig 2). It was, however, no longer compactly dispoeed; rather, it was distributed in a flocculent manner. Nevertheless, the total amount of dust in the lumene of tha alveolar ducts ap peared to be considerably greater three days after the intratracheal injection than that present immediately after the Injection. At the same time, Uas aabeetoe duet was ob served in the more peripherally situated al veoli. It is probable that the increase in the amount of dust in the alveolar ducts was de rived from the more peripheral alveoli. Al though some of the finer dot may have been intracellular, the greater bulk, by far, was extracellular, being imprisoned in tha inter- Arch. Environ Health--Vnl /v Nov 1967 Fxrt::: u'x< i- r,?n ;r/. 6u Fig 3 --Minimal moderately healed asoestotic lesion n rat enoosed to ctirysotile oust fcr one month, then oastureo and killed 24 months later Lesion consists of a oartiaily thickened alveolar duct Mural thickening is caused by hypocellular connective tissue that has ooHerated alveoli near bottom o< field (hematoxylin and eosir | y 150). <uces of the precollagenous stroma of the inflammatory tissue. When examined one year nr longer after the intratracheal dust injection, isbestotic fibrosis was found in all nts so injected The characteristic lesion was sharply limited to the alveolar duct as well as to the short re spiratory bronchiole and consisted of moder ate to severe collagenous thickening of the wall, often also associated with striking hy perplasia of smooth muscle in more than one third of the injected animals The col lagenous mural thickening involved much of the wall and resulted in the obliteration of many of the evaginating alveoli. Generally speaking, the involvement of the alveolar ducts, even in animals injected with but a Fig 4 --Field same as in Fig 3 after silver impreg nation shows that scar is composed on nonbranching, largely parallel, thick collagen fibars that ara fairly densely arranged (Gordon and Sweats. (X 150) single do6e of 3.5 mg of chrysorile dust, was greater than the minimal lesion observed in rats that had inhaled high concentrations 01 the dust for one month. As judged from the examination of a single section of both lungs of the rats, greater dust dosage was often, but not always, associated with an increased incidence of thickened alveolar ducts. The occurrence of larger collagenous scars con taming small remnants of air spaces seemed also to be related to the multiplicity of the asbestos dust injections, as was a metaplasia to the columnar variety of the epithelium lining the surviving evaginating alveoli The sharply delimited mural thickening of the alveolar ducts i Fig 3> and respiratory bronchioles, with the collagenized, nonarborescent, thick stromal fibers (Fig 41, and the associated reduced celluiarity (Fig 3i, Arch Emiron Health--Vol 15, Sou 1967  W 'i. r Fg 5 --Ash pattern cf acid-insoluble material of same held as in Fig 3 after microincineration and "eatment with concentrated hydrochloric acid showing ne presence of tangled masses of asbestos fibers in me regions of the scar tissue (X 1501 ''presented 3 healed nr healing mflamma - in Within '.his =o.ar tissue, apparent!1, w-questered compact masses of asbestos fibers were often strikingly prominent after microcc::i.-ration Fig '> On the other hand. 1 ; scars were seen that contained little or Inmnnstrahlo dust The sharp delimitain of rlic scars was accentuated by the aducent normal delicate alveolar walls. These were characterized hv single, nonbrnnehing irgvrophilio fiW-rs Nevertheless, in some of tne rats, there were also foci of a more active inflammation Such foci were marked by cellular thickening of llveolar walls and by lonsiderable desquamation. Here, the stroma was arborescent, the side branches tending to ji\e structural support to the increased num ber of alveolar cells Since similar inflanim.ator\ foci of cellular alveolar mural thicken- Fig 6--Hyperplg*l of smooth muiel* In rat miected twice with 3.5 mg chryaot. duat and killed 21 months later. Well defined bundles of smooth muscle are found m relation to alveolar ducts where the only normally present muscla is situated around mouths of evaginjtng alveoli (hematorylm am: ensin x 150). ing were also found in the lungB of control rats not exposed `n. or imected with. dust, it is beiimed that thev were caused hv un related spontaneous disease. No asbestos hodii-. were found in rats ex posed to or injected .v:th chrysotile asbestos dust. Rats 1 Inhalation ' --The characteristic minimal lesion, as fi end a year or more aft er the pulmonarv deposition of chrysotile dust, consisted of focal lollagenous thicken ing affecting patcho- f alveolar duct wall between some of evaginating alveoli Fig 3 and 4 1 With more extensive deposi tion of the chrv'Otile fillers, tlie mural fibro sis tended first to narrow the mouths of the evaginating alveoli ind then to close them 4rrl; Emtrnri [{colth --1\>I Voe 1967 ' ,v ;>r. rnr\ a t h. aw r'g 7 --One of smaller ceMu'ar *oc< t lungs -;f - amster niected twice "trar'acreadv *:tti 3 5 mg m'.sTtiie dust Ammai J.ea -ne yea' *ater. The ai*eoir s""jcture of cellular t.ssue s ooi -.erated bv cetiuia* crofferations. There 'S a surges' on of i pprypcid mass v ghtiv to the right and above t^e :*'>rer of the he'd ''e'-'aToxyhn and eosm v ;5G). Ftg 8 --Silver impregnation of same field as in Fig 7 shows a plethora of branching and interconnecting argyrophilic Fibers forming thick alveolar walls and protecting into air spaces as polypoid masses of van ous s'zes. Largest Dolypoid mass >s one referred to m c g 7. it fills the lumen cf alveolar duct fGorao" jrn Sweets. X 150) oil entirely The fibrous ilso dipped into some of the esngmntini: iKeoli. partiallv or 'ompletelv obliter.juna 't'l-in In this :iun ner. the respiratory bronchiole and adjoin ing .ilveolar ducts m.iv U-rome converted into relatively smooth walled tubes with few or no evaginations. Most of the wall thick ness of these tubes was attributable to the fibroticallv obliterated iKeoli (hat original ly evneinated from the former The cellularity of the thickened structures varied considerably depending upon the time interval between the dejmeition of the dust upon the parenchymal suri ues and the death of the animal. Tn the tlorid stage of the inflammation, as seen in a rat exposed to the chrvsotile dust for four months and killed two weeks later, the cells in the affect od regions were large and numerous while ;!-,e stroma consisted of an aroorescent net work of argyrophilic libers in which the cell were enmeshed. In time, the argyrophiin tillers became thickened, condensed, and loi their arborescence as well as their arirvro philia; the latter coincident with their col laeenous conversion Fig 4>. During this process of stromal maturation, the cellulari tv of the tissue diminished and the cells elongated to resemble fibrocytes. In some of the rats examined a year or longer after the dust exposure, there were, in addition to the collagenous foci, cellular foci of more active inflammation that had no ap parent relation to the proximal portion of the .I/,' K'l'.tfn Health--IV/ i~>, Aw r-g 9 --Ash pattern cf acid insoluble material shows `nat region of polypoid mass n areolar duct s dersew permeated by tangled masses ot asuestos tiDers Small er masses and aggregates of dust are found .n periph era' jived" and ome- a.r spaces fy ISO) Momuf Same ot these e> mav tL-o cun ':un variable number* ot i"u\re.iirphonucunr i-i Kocvtes. Similar r<*l!ul.r ' of active nr! urtmation were d-o found :n -eiry of the unexposed I.M -eratoi \ enntrol r-u if i.mpar- .Me ere Lur)_- Section-- gI ll eXPO-e.1 uttO month <>r Ion Her to heavy airxentr mnns ot ihrvsottle dust fxhibrrd mininol hbrottc pulmonary le-sinm one . ,-ir or ionser ifter the exposure. In uontri-t m out <>ne of -i\ rats exposed to the same dust for onlv two weeks were Mmilar cl'.inte- tounrt The otlt or fne exposed animals !iid Uin;x that did not differ from those of unexposrd rat*. In neither of two rots i xpmet: to the Mine dust 'or onlv one week, u is there anv . wrieno ot isbestotie ribrnsis I l and H monr'iu re-pev- tively after xpo-urel Mg 10.--Numerous luminescent asbestos ncd'es m region ot asbestotic inflammation, from 'be na g of a hamster that received intratracheal inieceon of ; 5 mg chrysotile dust and died I 3'i months later '.unstained section. 12.5/0 3 LeiLz ' i.iect.ve and 0 9 Leitt dar f'eld condenser x 150) ( "inp.in : w i i ur..- allot icld msolu ole a-h s.. ' -r. v e.ti.d i tions shortly aft er the ri'. \:--iire :t in.>enreu that onlv a 'mall fee:.on - : Mm- inmum at dust could ho seen in the in:< of r its hp or more ears after ; h< -xp-i-u:. \ crtheless. mi view of the ultraniie-ostxit-ic -ize of much of the chrysotile da.-' "a t .tin.*-f this method to demonstrate nmi ml dust in the tissue must nut he n - ..d to indy Me necessari ly' that no du-' present It is also of in terest tin: tl - -Mu-Id examination of the unstained <* e- with in ohiecnves was negatin' 'or 1 imir.esient natenal. even in reeions l.iter shewn to "Main \hunrlant icid-in-oluble mmenl e-h In the lungs of i nunur of rats exposed mi chrvsotile du-t two im.i-itu or more, there l ri '' / " " i;.- / f - i. r /,--- V 'ji 1 J ;m / EXPERIMENTAL LitTOS1S --GROSS & DE TREV1LLE 646 -ere bundles ui sniooUi muscle uit olten 'nsl Uuted uu.-m-s i }iiO V'.n.k Kss FiThese muscle hunoles were r .rpiv ilclimitixi ind related In ;re wall of n:' k< lied ,ii\euk.tr duets. Thev hud no oonrw it,-,n with tiluod >t l>mph ve^-cls nor ouid a relationship to the muscui.-ria of a ermirui bronchiole ne demonstrated. In the newlv termed connccuve tissue about some of the alveolar ducts and respiratory bron chioles, there were scattered cland-like structures. These pseudo-glands represent iurvtving units of the evagirtating alveoli that have become lined by tall columnar epi thelium, occasionally ciliated. No acid-insol uble mineral ash was demonstrable in the area occupied bv the proliferated muscle nbers. 'The regions, pervaded by the more reilular and active inrlammation, some con taining leukocytes, were also devoid of de monstrable mineral ash. Hamsters (Intratracheal Injection).--Of 19 hamsters. 16 died as a result of the asbes- touc inflammation that followed the intra tracheal injection of chrysotile dust. 'The three survivors had received only one injec tion and were killed 21 months after the im position of the lung dust burden. The aver- ige survival of the hamsters that had one intratracheal injection was I8T3 months, with a range of 1334 to 20`2 months. The animals that had received two intratracheal injections survived, on the average. 14l4 months from tiie tune <>1 the first injection, with a range of 121 - to 1612 months. The three survivors that were killed after 21 months were emaci.ited and niso had exten~ive asbestotic disease. Many of the lung sections showed exten sive consolidation with restively few patent air spaces. In other lung sections, the consol idation was patchy, seemingly concentrated about larger air spaces with relatively little aerated tissue between the consolidated por tions. The consolidated portions were com posed of masses of cells with vesicular round or oval nuclei--apparently alveolar cells Fig 7 . Leukocytes were not seen. Al veoli or larger air spaces usually could not lie identified in these regions except after silver impregnation Fig 8 The argyrophil- ic mural stroma of all air spaces in the solid ified regions was greatlv thickpned by ar borescent fibers that formed a loose network 1 ncroaching upon the lumens. Occasionally, .iie argyruphilic stroma extended info tl* lumen of an alveolar duct or a bronchiole a a polypoid manner, occluding it. The or. densation of thin argyTophiiic fibers to for a parallel thick fibers devoid of arborescer.'e and the transformation into collagen, cho acteristic of the lesions m rats, was not st- <t at all or to a very minor extent in thi-; hamsters. For the most part, the occlusion f the air spaces was caused mainly by mask'd alveolar cells, but the contribution of the <t gyrophilic stroma should not be dismisHcd. It should also be emphasized that Ln o-ntrast to the situation in rat lungs where ate involvement was sharply limited to the dveolar duct and its evagmating alveoli, there was no such delimitation in the hamster lung. Here, the cellular as well as the stro mal proliferation extended without abate ment to the peripheral alveoli, thus account ing for the diffuseness of the consolidation Following incineration, abundant at id-,, insoluble mineral dust was observed in the involved racemi. Many individual fibers could be identified: some straight or waw others coiled and forming tangled masse*. Compared with the amount of dust found n rat lungs, the chrysotile dust in the hamster lungs was much more abundant and m*-'*diffusely distributed (Fig 9:. Asbestos k ies were found in abundance throughout affected regions. They were considers smaller than those seen in human lungs were readily recognized They were seen under dark-field illumination with objectives in unstained sections Fig ! However, there was no parallelism he**-the number of luminescent asbestos io -- seen in the unstained sections r.i" n amount of dust found in the same fu-l.i efter microincineration. The amount of du-e ore*ent was much greater than might in- sus pected from the number of asbestos f*iie' observed. Most of the dust and the asbestos bodies were situated in the air spa-es. When observed within tissue, the asbest.n l-odies and the dust were found trapped u.thin the network of inflammatory argvrophilic fiber- and associated cells that tended to occlude the air spaces. Guinea Pigs (Inhalation).--Barely -og nizable, minimal mural thickening of an oc casional alveolar duct and respiratory bron- Arcn Erutiun Health--Vol 15 Sot- 1967 040 / ` \ a i - * 11"'1 ." i- - ,1 *- ......... re '; f! < -:.i.,-r* o.- I.. Li;.- t* ' . p; < * no. : 0 -ioi'..= in r- i mural k< n i I i.= i - tec I i : : ri i!.. . . ,!<= : i - . -: dll' ,i : . Hi- r :nl. r< nm n _ , i,-,, .if- ::i,r . . : . Mg = ; it ; ,d i-i.r. >."i* . -* i:n .,! f .r. -ou!i ii : ' *r - ah". '.-.i.i r : unu'estixl -.tnii.ir * .; ,.iI hi ii il ^istolk i:u> hem rig m the - =..... 11 [mi,on n| * io r h-i-mils f I> >* v. c r. number ol jna.s * tccmi involved was k/i cro.iter than :h.u in the aiunuis ex *sed !o the !',,'ait du-t concentration for lav inontlis. No evidence of healing sig- m.int reduction in ceii'jluntv of the levion "4 eoilageni- in n of iin v-romu Mas seen .:i .niriaU c\ .iiiinnj 'if> 'o -even ii'onth.s aft er the .< gaming nt ;! ; . \;.x,-ure. Following microintinrr iiion and treitment with acid, he ni ant < ' ash seen ,n die guinea pig hmg section.- was i ompar *ill to lh.it noted " r.lt.- that i: id ililialed < i>ry-otile dust. As 'e-uis ;iklfound in the iting -actions were few anti -. erv -mall ( onUTU'llt V i -ironic i.uimun.irv inilammation mav *d proerer.-iv r 'f .t c\trnds from its ritin.ii -no into adj,oiunL', previously nor mal ao -prices, old if it remains active, re taining its arg> 'ophtiii : 'eeoilagenous stro ma and Inch o llul.uutv = jrh a puimoa tv inil.onmation mav is* ci-n.j.aerod homed if 1 * - irgyrophihc -Irmn.i h.i. I en oornpletelv ...igcni/pii wi';! its pclltj a ;tv iii- In-come considerably reduced. fn the rat ih a ha- inhaled high, conceiti'ioic ol ehrv-"(,!e .,-iv-tus nlx.*rs tor only f'a months or ha.- 1-is n ,incited intr-i trncheallv with tins du.-t. the i-hestotic ;n:l.immation remain - sii rpiv limited in the proximal [rtion of the mcemus anti heals hv hecoming transformed into a hvpocellul.ir collagenous scar Tlias t would appear proper to classify a-l**=to=i= i .used hy thrysotiie dust as nonprogressive in the rat. It is of basic interest that appreciable amounts of asU'stos fibers are demonstrable within the -cars of healed . * healing infl.unmntion This would suggest that the - .v l E T,=?'. ll.LE | px-ar .ace t rtr\ ~otile dust from the - u. i cur i G. .-oiut;pn or hv transport, a t a -'me mu non of healing; but that a* -iiing, at U-asi in ;ne r.a. docs take place-- u,,i in the pre.-ence of tins dust. One would Ac to think of the umiatiun of the asiiestos nody as a protective mechant-m hv which t! ,c i-besto= til* r ix-comes set^ui-siratcd and 'lie tissues safeguarded from further irritant ictiun hv ihe lilx>r To what extent this nux harusm mav apply i3 not known: but it does seem that in rats, in which asbestos liodies are nut demonstrable with the opti cal micro.si|ie hcaiing occurs in the pres ence of apparently naked fibers. The diminution, in time, of the amount of dust demonstrable in the tissue and its ippurcr.t disappearance in some of the scars, ixis**s an interesting question in regard to the mechanism hv which the asbestos fibers disappear. It i= commonly believed that chrvsotile liber-; have a relatively high solu bility in ti.v-ue fluid. This would seem to ac count for the inability to demonstrate ashes- tos fibers in some of the asbestos bodies found in human .m-U siottc lungs. However, dissolution of the libers, particularly of the courser ones, would rc-quire a long time--so that it a aid !>e difficult to explain the fail ure "f peripheral alveoli to become involved by inflammation Furthermore, high solubil ity would nin* consistent with the sharp inflammatory oc.i1//-.i tic in of the asbestotic lesion in the priviii u portion of the raoem- us in rits It i- u.'j*- -nurc reasonable to explain this sharp iii/aion of the in flanimation on a tairi*- uro'-ipt removal of the inhaled or injected irrn.,rit dust from the (teri[)her u ilveoli anti the - tbsoquent stag nation of the dust in the proximal portions of the racemus." The .rnn.-mrt of the chrys- ottle dust from the (x-ripheral alveoli is ef fected hy the alveolar clearance mechanism consisting of a proximally moving film of tlveolar fluid.6 This transport Ls dramatical ly illustrated by the increase in. and concen tration of dust in the lumen of the alveolar duct within hours after the intratracheal injection of chrvsotile dust :cf Fig I and 21. It may be of interest at this point to note that the localisation cf the early asbes totic lesion to the proximal portion of the r tcemus was first described by Vorwald et al.'* and recently confirmed by Holt et al.* * r* n F.i. --"'I U> aith -- Vol 15 Xor 1967 oo cn /-.X."U sdf.s/wM'S-^TOSa i- DE TREl lLIE 641 [ ' w re -clloll ol ll.r n.ini-1*- mug t.i . ir cJiL-t i: I he mtsthcMs of th.it . .->s :\ru :i r i:~ The lesion . \ tends from :ne \ - t>:imil [xirtion of the ram mus to the pern'hrval itNfiii. ! 1 u`rtny prodm ::s4 exter.rive >'>n<,,: ijt.oni m the hamster nines. The lonsoiniann- are composed ai hiiterated air cn.ice'!;e hir.iens ot which are tilled with masses of ih,-oljr cells, mostlv desquamated ' Kip b . Although the inflammation involves the er. tire raccmus in this animal, the proximal portion shows more severe involvement than the peripheral jiortion. It is this ex tensiveness of asbestotic involvement with consequent pulmonary inadequacy that ac counts for the high mortality of the ham sters With the previously given definition of progression in mind, it is seen that the diffuse involvement of the racemus in the hamster would fit the first requirement for proitressiveness of the disease, if it can be ihown that the inflammation originally was confined to the proximal portion of the ra t-emus and then extended into the peripheral air spaces. This information, unfortunately, js not available from the present investiga tion However, the finding of a more severe involvement of the proximal portion of the racemus favors the probability that such an extension took place. The second require ment of progression, ie, that the inflamma tion remain active and nonhealinp, is a con spicuous feature of the asbestotic hamster lunes The failure of the argyrophilic fibers to lose their arborescence and to collagenize ..nd the persistance of the extreme eellulari!v of the involved tissues nearly two years lfter the intrapulmonarv dust deposition is incontrovertible evidence of nonhealing Two possible explananons come fo mind for the difference in the disease produced in the rat and the hamster by the same chryso' ile dust. One explanation is that the reactiv ity of hamster tissue to the dust is greater than that of rat tissue. The other is that the hamster's alveolar clearance mechanism is not as capable as that of rats in transporting the dust from the peripheral air spaces proximally. As will be seen below, both explana tions apply. There is some evidence that the hamster's pulmonary clearance mechanism is not as effective as that of the rat. This is seer in t ie considerably larger amount of icid-insol life mineral ash demonstrable in :he ham-ter lung sections than in those ot rats Fur ther evidence is seen in the diffuseness of the dust distribution in the hamster i g `* > in contrast to its restriction to the proximal portion of the racemus as in the r it Fig oh The reactivity of hamster tissue to chrysotile fibers is significantly different In in that of rat tissue, the former being much more florid. This is seen not only in the plentiful production of asbestos bodies in hamster lungs but also in the failure of argyrophilic precollagenous fibers to mature into colla gen as well as in the undiminishing cellularity of the inflammatory tissue even after a lapse of nearly two years. This difference in the reactivity of lung tissue in the rats on the one hand and in hamsters on the other is not unique to chrysotiie dust inasmuch is simi lar and quite comparable differences in these two species have been noted in their reactivity to quartz dust.10 It is highly probable that interspecies differences in the efficiency of the pulmo nary clearance mechanism play an impor tant role in the susceptibility of the different species to certain pulmonary diseases. It is recognized, for example, that horses and mules working during their lifetime in mines exposed to quartz dust will have accumulat ed a negligible amount of silica in the lungs and will demonstrate no silicosis;11 whereas miners in the same workings will have vs.-v ing degrees of silicosis as well as a sig nificantly elevated pulmonary silica content. We have recently exposed rats and mice imultaneously to quartz dust in the same -ihalation chamber for the same length if time. All animals were killed immediau-iv liter the end of the dust exposure 'A. I defined silicotic nodules were present in me rat lungs; whereas, the mouse lungs wt-re esolutely normal, and no acid-insoluble dn-d could be demonstrated in the mouse-lung sections after microincineration > unpub lished data). The above observations are relevant n> the present investigation insofar as such ir terspecies differences tend to make extrap*, lation from animal data to human disea-w unreliable. The questions to be resolved a* whether the efficiency of the clear m* mechanism of man approximates that of tl* .Arc/i Environ Health--Vol 15. Sov 1967 r AO;.,' ' ' (.iff .V ;>h nu v: ' !.'r r>49 ' The < h.ir.H tcrtstic c.irlv .i-1> >-- t.jt:c !>,un is situated in. and sh.irpiv localism m me proximal portion of the pulmc.in.ry ra'em us Ahirh. :n the r it. p insists it a ter'. -ii"rt respir itorv brenc h:->!e m.rl ..i'.otmng iheol.ir durt> _ A-t'-t'iSIS in rat', c\,u-'d bv ch-v-otile lust - nonprngrcsMve ! The t-wdenu* for the nonprogressiveness of chrysotile ashestosis in rats consists of the nbserxntioHs that tlie minimal asbestoiir le-ion is limited to the tsall of the respiratory bronchiole md of the adjoinin'.: iKeoi.ar ducts and does not extend into ad!"intnz normal alveoli and that the minimal ,.'hMoti< V-ions heal hv becoming collagrnt/e'l .nJ ns tmiv llular 1 Tro localization of the minimal asbes' a ;< -'-'ons s attributed to the proximal Tm-norr of dust from peripheral air spaces is In' aiseolar clearance mechanism and ,-ulisequont stagnation of the transported dii-f in the proximal portion of the racemus. I In rats chrysotile i-bestotic lesions hed in the absence of demonstr.ible optical mu 'i.-oioe asbestos bodies and in the pres-nci i' hrssotilo libers, the latter liecormng r.ijii'--: n the scar tissue. A There is a considerable reduction in the amount of chrysotile dust found in the hing .stations of rats one year or more after the imjHtsition ol the lung dust burden as iTin ;-1rod with the amount of dust present -horttv lfter the dust burden was imposed. Hi.' reaction ot hamster tunes to chrvs. ottle dust is the antithesis of that observed ,n - its 'Pie lesion is progressive. extending into [ien()her.d air -paces -o as to involve the entire racemus and thereby producing x tense. isaix ilidations leading to the do ith of the uuin.ils. The lesioru do not hed. -inee the precollagenous stroma and the nigh eellulnritv persi-ts through the tun ear [>eriod of observation At the same time, the amount of asbestos dust demon strable in the sectioas remains large and .luTu-eiv distributed. * The progressiveness of the chrysotile astx'Stotic lesion in hamsters is ascribed to a less effective pulmonary < lea ranee mecha nism ind to a greater reactivitv of the pulmnnarv tissue than exist in rib 1 The carlv chrv.-otilc *tio ie-.nn ,.t guinea pigs resemble-' rf..it ' t.-. l'U` it has not lieen adequateK -tudieo 'o permit y.irthor characterization i"his *fw<K w supported fi f , 1 !>* -p. i< e Ki.tni OH 0*132 John, \ tti ''much *`-p * ourtrA <.f Ki n:;' i1' i|'()tt-<l :'<* < hr\sofd<' I >.,< H* , i:l t' in (Mir ** mh MT References ! Rosa, W D . r-i .il FmotKwi.tl < * of Rcapi rxforv Disordets Among G Ml \lm< rv /AAfA 156:484 'Oct 2> 1954 2. Holt. P F . >md Ymmc. 1 t K Dust l ift Mechanism Suitable fnr Fibrous Du-: \rn Ot * .i Hyg 2:2r. 3. Wright, RM A Size Selecting Sampler i Air-Bome Dust flr:t J \f*'d 11:2*<A 19V1 4 firoiR, P. .tnd T'lki-r. E R Dust f t - n Lung Sections Some Notes >>u Method- Visualization. Ar.o, Enitr^n Health 12:21 5. von Hnvok H The H-.<nnn Lung. V 1 r 'traasL New York Hnfiu-r \ jblishing (.'-(. [nc. p 1 "2 6 Vorwald. A J Durk.ui. TM and Pratt. Experimental Studies of A.-vbr-stosis. Arrh lt '< Hvg 3:1. 19M. f.rnss. P.. Pfit2er. E A and Hatch. T F. \ veolar Clearance r*.s Relation t' Lesions of the ft spiraton. Rroneluolo \rj.-r A' R-<p Dm. 94-` 1%*. Hatch. TF uid Onws. P Pulmonurv D po tion and Retention of Inhaled Aerosols. New Fin Academic Press, Inc . 19*V4. p o9. 9. Holt. P.F.: NfilH. J. and Young. DK T ..r - F.fTects of Chrysotile Asbestos Dust on Ret Liin^ Path Bact 87:15. 19*4 10. Gross, P; deViJJiers, AJ. and deTreNU*. RT P Fxpenuu nii Sdi. osis. Arc/? Pafh 84:^" v l ^7 11 Embrodt. H I Klo-iei Knitcr and H . Verleichende l.'ntersuchumren uber die V t,'M's4on rrtimerter uN>- in d^u I.uniren on Nti und Tier Seitr .Snifiuj- 'urif/j 6:4l. 1A.I 12 Gross. P . and Smith. K W Fhe 1' jno^r - 1 )iNf, d-uf ton of Mineral DiicK in Son- I'n* onioiic Lungs. Dis ( J5 ! M) t *rt!* 13. Ciosa. P '^,tholo|^^ f>( the Lneun'** n loses " m l^n/a All. nd 1 / h>' f'ncu r^ncnn > New York: Grune and Miatton In< . !'A p 14. Knox, J F . and fl. ettie ,f Minersi of the Lungs After FxjKr^ure o \sbe*lo* I Ki fndustr H*g 10:23. 1950 15 Nagelsrhmidt. G Some Observatiorw r.t Dust Content and G0nip*iti`<n n f.unga With hestosia, Ann NY 4<ad so 132:64-78. Ta`A 16. Ray, SC.. King. I' J and Hamsoii ' Vr i Action of Variable Amounts of Quartz vn *he 1 1 * of Rata, Brit J Indu/tt' \fr,{ 8:62. 19*1 17. Siebert. F T and Fisher. E.R: Rnmciu- r Emphvsema. At* *r / !`,:th 33:1137. Uf-r> * \r*'E h '}> ^r<<n ffrotth --1 <>/ \ot 1967 ;n ro I irv- r**4 S A J'H NXAI I 'I l SWUtAfllRY SSI) ( I l*< < M VO I 'll \; I \Pt RIMI NTAI. STUnil S ON ASBkSTOS PLAINTIFF'S EXHIBIT I M I vi.i l KIM ill / >< /uirtnu n! nf Pfivuo/ocv. I mivni/v III \hllinhii\ili __________ DOW-1455 s,".i i'h . ol (lie I'rK-umoioruosis Research Department of (urology. t'nivcrsity nf Sieffcnbosch f i " t m i.'h.inmvl'tng m |`S4 mvcsliu.itions have been ashestos fibres were isolated, cut tip as finely as poss. "i.l< m il>. M i.i .iM.irl.un uhi-lhcr pulmonary lesions anti ami ground for several days. I he rock crystal was erto .""I'liv itiiinv tollowini; the inhalation of crocidolite anil and also ground m an agate hall mill I he size disir "''Mil- .IiisIn wi re vmnl.ir to lh*se .ism's latvd with ex- tkm of the particles is given in Table I. A mixture I'-'vnii t.i JihmuiIv iluvt 1 | he results indicated that , i.n nl,'hie .mil .mtoMie dusts essentially caused an interoiimI iihroMs, ihi\ May seen In he pen brunchtola r and tam t ii. <in ur ai anaiysis oi iprmnm (from VermaasMt ixri\.iM.nl.ir in distribution during the early stage*. and in tin later stages the lesions became diffuse, with alveolar "all thickening and peribronchiolar and perivascular tiKr>\iv Other clinical investigations suggest that ashestos may he SiO, AI.Oj Fe,0, FeO MgO 51 94 0 20 IX *4 19 39 1 37 Ca Nad) K)0 h/**H.O Total 01 A0 'o 0 oa 2 5> 100-7. implicated in the development of malignant tumours of the pleurae, ami primary neoplasm of this nature have been inscribed bv many author* in recent year*.1' The pathological e\idence associating these tumour* quart* and asbestos was prepared in the proportion 25:75. The chemical composition of the crocidolite axhc is given in Table il. ___ m ith aybeyto* appeared to be inconclusive. Wagner.1 how Animmix. Albino rats {Rattu\ nnrvrgicwr. Wistar lr e'er. reported that 47 case* of mesothelioma had been tute) weighing 150- 175 G. were used. Two group* of iilcniihcd in South Africa up to the end of June l%0. In animal* each were injected intratracheally with suspemi 4' of these a possible asyocialmn with exposure to crocido- of ashestos and a mixture of quart* and asbestos* rest liie (rom the Non hern Cape ha* been established. Whether tively. the primary factor in the development of these tumour* i* esposure to asheytoy dust, or to a contaminant of it. i* a* set not known. According to Wagner, one would expect similar cascy from the Lydenburg district, since the nature l the rock, ore and fibre, are almost identical with those of the Northern ( ape. Mu-mpis to produce tumour* in experimental animals hi exposing them lo an atmosphere of aybesfos dust or to 'nir.iiraclie.11 injection of ashcsim have been disappointme " ViirMnlil rt nl 11 found Hint ordinary industrial .ishvstoy dioi and lonu fibres from which the small nanicies hail Seen separated cave peribronchiolar fthrosis. With dust particles 5,, or less there was little or no reaction in expefi* mental animals. Behrens'- also reported that pure chrysotile jshestos injected intraneritoneally into mice and intratracheady into rats produced only a non-specific fibrosis that michl be due to a foreign-body reaction. At present no Dim noprnWom. The dusts were suspended m o saline in the proportion of <0 mg. of dust per I ml I samples of each of the dusts were weighed out in s.r capped hottlcc 20 ml. of saline added, and the xuspen sterilized by autoclaving for 20 minutes at 15-lb. press The suspensions were shaken before use. infrrtutft nf <lu\t\. The an mals were lightly anac-iltd with ether. "Ibcv were ncd on their tacks on a sf*( dissecting hoard f 45 ). the longue retracted with a < a speculum introduced through the mouth into the thr and the head drawn forward and downward until ehorx's were visible. A 16-gauge hlunt hollow needli inches long, was then inserted into the trachea: a *yr containing I ml. of suspension and I ml. of air quickly attached and the suspension injected forcibly the lungs. evidence is available renardtnc the nuthogenicitv of croci- Dhratinn nf rxprririrtit. The experiments lasted dolite m experimental animals, although clinical reports days and one rat out of each group was killed at incriminate crocidnlite as a possible aetiological factor in the development of malianant tumours in the lung of humans. The present preliminary study was therefore planned to investigate the pnihocenicity of crncidolite and a mixture of crocidolite ami quart* In the lungs of rats. intervals. A few animals died and had to b? discarded Hiuitinviral rrrfmltfttr. The animals were anacvlhv! with ether, the trachea exposed, and It) ml of formof-salmv injected into the lungs b'- inverting a iw needle into the trachea. I he tracheas were then tivd rmc i. si*r otantmmn* nr PAannex op ranrtooLm AXO gUANT* CrocnMItr Quartz the animals nutnpsicd. and the unopened lungs preserve 15 formol-salme. After fixation, the lungs were secIn in a sagittal plane near the hilum and whole lung hi were embedded in paraffin wax. Serial sections of V 20 V Ml 2/4 40 1/* 50 10 90 50 50 thickness were cut from each block. Of these, two ' stained with hacmatoxylin and eosm and another imp nated with silver (Gordon and Sweet1*)- The rcmai sections were kcjst as spares. mstfrialm and method* Grading. The grading of the maturity and scvcnc Hum Samples of very pure rock crystal (quart*) and the lesions was done according to the new system of I ft n\ I' si follows 1 S A I r I >stk X l| \ lit I.AI* > AI< iw H *1 l s K M'-11 k .' i i .? < . > . ! t:br.`*` I .-xf ri-ltcwlt" riM i i'II.I < <>mpui rctktllm wilh *iih<<iii t"Hagen k.Ttuh.u icllul.ir hut i".u!c up mostly ol colla- rvu " holly uwp'ifd of col- I iccn iibrex and virtually ,iv cHular \i dltil.n. yi'lt.nenoux. <.innucnl 'mi'iini <<f /ihmiit Vcrv few n*dulrv Few nodules Moderate number of no dule* Many silicotic nodule* Vhestos duM alone was readily tngrted bv ihe rru<.r.' phage* and tran*ported to the vicmitv of the 'mall Won chtolt. wliere big aggregate* of du*i cvcntuilly accumu I *rge area* involved arsn is r,>\r'>ptc A pprarrmm Mucro^copn; examination of the tunfr* of the animals the avbcvio* and quart? asbestos group* 'hoard no iivt.imlmi: differences over the first Itift day*. The duet 'inhiitHvn between the two lung* tended to he irregular, nd more duM apparently entered the left lung than the chi lung. I oci of dust were xeen on the xurface of the me*, hut no ftbrottc change* could he observed. After I no day* the lung* of the quartz-asbestos animal* u-amt firmer and al*o larger in tin compared to the mg* of the a*be*to* group. Area* of fihroxh. particularly <n the doeval a*pect* of the left hmg*, were seen while in he a*he*to* group the lung* remained *oft with only a i w minute le*ton* visible on the pleural xurface*. \ftrmicnfHr Appetirtmerr The grade of fibrosis and the amount of fibred* pro duced by asbestos and an axhestox-quirtz admixture in the lung* of rat* over a period of 220 day* are given in Table III. T*m r n on adc and amount or rtenosi* moooceo y Oli vros ANO AN AMUroiOUAlU AOMIXTURt IN TW* LUNOt 4itu Ku Or nT* Tt | Q_j_ G-aWa? jhmmmml mf ?" I 4>t i o l .o : mi i ii.wn 1i i vi ' iw yr> : :.*> i `INKiin can >A imftaimm Tutu! 2* 2 ) J J 2i * i 0AM tf AMMf I t I I t 2 2 2i > 1 Taut The pathological changes caused by these taro dust 'ample* followed more or le** the same pattern over the fir*t ton dav* after the intratracheal administration of the du*t* Some difference* were observed concerning the cell type* involved, the rate of phagocytosis of the dusts, and ;hc *itc* of M**ue reaction, a* well a* the incidence of infection. <)n the introduction of both dusts a typical foreign-bodv reaction was found. The reaction in the quart?-a*he*tos group w*x more severe and numerous mononuclear cells and leukocyte* were mobilized, much more so than in the lungs of the asbestos group, where most of the asbestos particles were phagocytosed within so day* and relatively limited ceil destruction occurred compared to the asbestos-quartt group, fn the latter group omr avbestos and quartz particles were found lying free Fit. 1. Long section ahowing numerous macrophages loaded with asbestos particles in the vicinity of a bron chiole. with some alveolar wall thkkcnint. 60 days after the intratracheal infection of 50 mg. of pure asbestos dust. (W. ft E. x 45a) lated. The dust lesions in the asbestos lungs were therefo primarily encountered around the hronchioit and to lesser extent in lung areas with a relatively high conce tration of dust. These lung areas were well marked alveolar wall thickening and the accumulation of numerr macrophages and giant cells, loaded with asbestos partic (Fig. I). The quartz-asbestos mixture, on the other hat provoked a general and widespread tissue- reaction which the hronchioli. blood vessels and alveolar walls w< involved. It appeared as if the presence of a small cooct (ration of quartz interfered with the phagocytosis of j dust to such an extent that a diffuse fibrosis resulted. Hyperplasia of tha lymph nodes of the lung sms i common in the asbestos group except in cast* w infection. In the quertz-asbestos lungs the nodes appea to be hyperplastic and infiltrated with fibrous tissue. The incidence of lung infection in animals injected v pure asbestos tended to he higher than in those wh received the ashestos-quartz mixture. From the histolog sections it was observed that the hronchioli of sev. lungs infected with asbestos dust were comply blocked with mucus and infiltrated by leukocytes, mat phages, and mononuclear cells. Dust lesions in these I areas, notated from the respiratory tree, showed a mar increase in collagen content and progressed to grac fibrosis (Fig. 2). In animah without infection the prog aion of the I--ion* was relatively slow and they reac only grade-1 fibrosis after 220 days (Fig. J). fn *h quartz-asbestos group an acute infection s \ 11 'i .<s m . i I mu im \ may \s|j ( i isi( m Mi i hi isi ' : i i\ "'H .1 miiii.iI uni i'u iiHu'iiv. Ji.ii'li' in this . . , k. i . I n.< ' i 11 m i m. .1 in 111 .Imtit 11 i.. mi 11 in hi M n.. ...... Hu pi in'ii vsii.ii ni 11 it- liMimv m tins pr imp was produces! in Itin period (I ig J ii>ni[%md In j nrjiJt anim.il> vmIIiimM ini linn, m I in ,isix \t(>s i-rnup No malignant Uinmurv nr .on neoplasms ol Ilic p1 f iv R.o limn wiih infection. 2hn days after the injection nl sn mi i>f asbestos dust. showing grade-2 fihmsis. (Silver impregnation * I Vl.) Fit. 4. Rat lung section. 200 days after the injection dual consisting of 12-5 mg. quartz 375 mg. aahesn showing massive grade-3 fibrosis. (Silver impregnation 150.) o sfcpnonaiiv mow up to !00 days, a marked increase in ,. i .i---,r.-, ..H .h,, nf ih Fit 5. Part of lung section. I Kit days after iniectmn of quartz-asbestos mixture, showing pleural thickening ' mononuclear-cell infiltration. (II. dc E. < I5<l.i were observed, although pleural thickening was foum few cases with infection and in most animals imc s\ I ;M I V IK IMT'KII M. IN KllNirv\MK '7 hiwf i 1 ' . c 1 ii . n .'I r i I n. 11111 m Ilu I'imi'n o' f.ils inn.-i.Hll lit 'mi i.S'ios |\iili<.li' iihI ,m ,isHi\iii\ qn.irt/ .iilmis- 'i ' I ' I....... . In illlllf 'Il'mlK.llllIv 111 llic I.iUT si.igcs of "i (ViNimuMi In ilu ,ivht'-ti's t|u.irt/ group ;i progressive . t,i't- - I niitiilin .mil toll.i^eti in llie dust lesions wax 'hihiI 'I'liUme tcrnun.illv in Ihc production of com-'ui i'iMiiIU .it illitlar. soll.ievnoiis nothilcs In Ihc i-'i'iip progression of llie inili.il relieulin was ' t111it () .uni i! emletl with onlv slight mere:!sc in compactn. ss vtiili m \\ it lii it ii ,t levs line eoll.ipcn lihres in eases " illi it nle mlevlinn llie pn'tnl results ilernnslr.ite lh.it line ashcsl *s parI'.les ,ne i'i .i vers low tovieily lo lung Iismic anti produce >nls perihronthiol.ir, ami to a lesser degree perivascular, ntitiilm nefvsoriis I sen in caves with acute infections, lihrocenests tlitl not nrocress beyond gradc-2 fibrosis. The upit.il .ishesiosis of hum,ins coultl not he induced with port line asbestos dust m the lungs of rats. However, the addition ot viliea dust (12 5 me I to the same asbestos dust i 17 < mg i led to massive fibrosis (advanced grade-5). Both the maturity and the amount of fibrosis seemed excessive when compared to the lesions causes! by equivalent amounts of the mdivitlu.il dusts. The microscopic pattern of the pathological chances appeared to he very similar to those described by (ilovnc|r and Lynch and Cannon17 in humans Houser rt nl '* concluded that the common factor in the lungs of miners of asbestos and iron-ore is silica and it is suggested that this may be the carcinogenic agent, causing pulmonary fibrosis, which nrecedcs the initiation of the malignant process Doll* also pointed out that the risk of lung cancer in asbestos workers was of the order of in times thai espcricnecsl by other men. Probably this risk vsas greater before I17'* and has become progressively less (lurmc recent years as the durntion of employment under the old duM> conditions has decreased. The fact itut no malignant tumours have been produced h\ either crocidolite asbestos or a quanz-asbesios admix* lure might be due to the very high resistance of the rat species to neoplasms, as vscll as to the limited duration of ihc present experiments. However, it appeared that free silica enhanced the pathogenicity of asbestos dust and that in the presence of silica some pleural changes have been produced, although not of a malignant nature. Recently it was pointed out by Harrington1** that oils containing V4 benzpyrene and related substances occur in crocidolite and amosite. The significance of the association between asbestos fibres and hydrocarbons on the one hand and the production of malignant neoplasms on the other hind could not he assesses} from the present experiments. because weathered criKub'liic has been iivniriMvkuh hydrocarbon content might have hren extremely However, it is doubtful whether the concentration of ben/pyrenc in virgin crocidolite would he high* ewougt produce neoplasms, seeing (hat coal dust with a retail higher concentration appeared to be inert The present results support the conekroons of Bo rt alS* that silica in combination with asbestos may extremely dangerous. SI'MMAXY 'Ihc pathogenicity of pure, very fine crtkidoliterparli ami of a mixture of crocidolite and quartz.'wa?in*e<tigi alter intratracheal injection of 50 mg. of theso-doxix- the lung* of rats. The proliferation oferdfciifNtedue these two dusts respectively was found*' cantly. The crocidolite particles elicited an mMihlff that became slightly more compact. wtihHor*rith collagen fibres, especially in cases withr" appeared'that exposure only to axbcstocH to acute* respiratory infections,- - The asbestos-quartz admixture gave: aymteam creaxa- m retkulin'and .collagen^ 11 acellular collagenous nodules fgrade-^'fihros^CTTiif hi logical picture of the pathological changeMppeami tn very similar to those observed in human* asbesti Asbestos dust in combination with a small amount of silica should be regarded as extremely dangerous. No malignant tumours have been produced in experimental period* by either axhesto**us:the*ashes quartz admixture. Some non-malignant pleural char were observed in animals of the asbestos*group.with' in (ion. and in animals of the asbestos-quartz group. at.rtxi.NCH -r y v -*'< _______ _ I. WINitirMiwfirimi.UC'li. fIw irWkMifiMr,W/MAm. iwJ.iAwsd*. . Ia.- . 2. Tn*a. O. llVSSti At path. "mitti i. IfcWiiiil. O md a<v (1. ilssTi- A<1 4. M. C. IISSTlr ClMf iXhllad.l. I.JV s M.< 4iihrv. W. T. iis<*l: j Fuh Hj.i . 7*. 517. s. Wi*rr. I WlV C A. isJ MinSmIi X. (ISVS- Sn ImIimi. Mol., t7. 2hi 7. I tmli, K. M flmHh. W A. HUM' Amr. I. Cancer. 24. 4 II.HI. X. (tsss). Hfil j. ImtttMt. Med . 12. l . Cjdtvr. X. (ISSJI-. Arch. Index*. lira., *. 2*2. to. VnrwaM, A. I. and Kar, I. W. mill: Auer. I. hlkn 14. as It. VnrwaM. A. 1.. Owta*. T. M. Md Fruit. X. C- Indus*. Ht,, J, I. It. IWOreus. W. |*SI> XthuuW. Z. Xi . M. 27S. I) Viiwm. F H. S (1*721: Ttn. Owl. Snc, SWr AWu *9. tvs 14. (Mm. H. end As1**. M. II. Am. /. Mk. It S4S. is. Kim. H. X. Ktnt. F. i.. Viewlhan. M. w4 MuuimhniiJi <ISA2): Ann. Occur. Md.. . I4S. IS (itnmc. S a f test lancet. I. *40 17. Lynch. K. M md Caiman. W. M. (IS4SI: I O'. Chew. 14. 474 14. Aimer. O. M., t-euMv i. X. and .them. M. I. llt|: An Clin. F1h . 29. 12*. is llarrlnfon. J. S. ilWJl: Nature lined ). 1*7. 4t A C ASK OF PKRSISTKNT THYMUS DIVF.RTICULA IN THR NRCK J. A. Kiin. ncpanmrnt nf Anmtnmy. University f Cnpr T>*n I Ik- fxrv'Hntc uf stalks of lliymic tissue in the neck, .icmunsiraimg ihc cmhryological origin of the thymus gland from the entoderm of the third pharyngeal pouch, is undoubtedly a rare condition. In the course of 50 vrarx' i-sprrit-ncr of UMchmr inxfrunv this is fhn first dissecting room. Descriptions of such a congenital abr mality are absent in many stamlard anatomical . cmbryoloficai text bookt, and only a few references ci> ne found. In Braus' Anatmnie Jrx Memehm (I'i. Here is a schematic and hypothetical drawing of the n