Document DMzjJQXk8QX3oGzG46VdM9myN

c continuously, until aaci 1 fi .:cd, tho exposure period ranging from one month to nearly 54 months. Tho othor two were removed to normal a* after a duot exposure of 31 monthoj one of those was sacrificed 6 months, and tho other Jl-l months, later. In gonoral, the tissue response urea con fined to microscopic foci of fibrosis in tho Trails of groups of subpleural alveoli, rathor tlion in the peribronchiolar areas. In one animal the change was extensive enough to be visualized on gross inspection of tho soctlon. Only in tho animal with tho longest exposure^r-54 raonthn^-did tho X-ray revoal definitely abnormal shadows. After 30 montha tho pS- ture was nogativej aftor 45 months, a faint mottling oould be detootoif* throughout both lungs. At autopsy, 9 months later, there was only microsoopio fibrosis In tho subpleural-cone plus heavy lymphocytic infiltra tion about small bronchioles. Anbostosis bodLeo were raro. On prolonged iH- aoarch a few yellow atypical bodies, smooth and without haunt rations,-^' woro found in two animals exposed Cor more than a year. Reaction in Rabbits. Eight rabbits wore exposed to dust for periods extending from ono to more than five yearsj tho last animal was removed from tho dust room and left In normal air 6 months boforc being sacriflood. Thoro tm never enough pulmonary fibrosis to bo dotoctod.grossly and.thero was no chronic adheoivo plourioy. Miorooooplc evidonoo of alveolar wall thickening was first detected in ono animal after about 3 years of expo-- sure and was socn in all- five animals oxaminod thereafter, including t|vtj , \SP cno removed to normal air. One animal, that died of paralysis after noarly fo\r yearn of exposure, exhibited a reaction visible on gross inspection of tiosuo oootlon3. Tho possibility of pulmonary infection In this -21- 4*