Document 5boRRxgRBe0p12q15r0LkGBJN

c;*\ in the atmosphere breatlioJi oooond, largo particloa are more effectively removed by the protective nioahcnioran of tho upper respiratory tract. In the cano of fibrous mntarinlG thoso faotore have lees Influence and fi ber a 100 and ovon 00 microns In longth havo beon found in tho terminal air spucos of human lungo. In small laboratory aninclo exposed to aobeatoa dust tho maximum length of fibor found in tho lung raroly exccods 60 microns A largo proportion of non-flbrous partioulate dust inhalod into tho lung Is found in tho terminal eir spaces (elvoolar duct, atria, alvooli) in all parto of the orgsnj in contract, inhaled ecbostos fibora are .first diecovered in the respiratory bronchioloa. Thooo rraw.ll passages aro im mediately distal to bronohloloo lined by oiliated epithelium^). Thoir own essential lining is o low cuboidal typo of epithelium but, as thoir narno iraplios, thoy actually function in respiration through lateral alveo li distributed along thoir walls. Either these alvooli or tho abrupt chongo in the character of the lining epithelium'or the email diameter of tho rooplratory bronchiole or the combination of all three factors is re sponsible for retention of the fiber at thin olto. Only after asboatosic is woll ostabllshod are apprcclablo nuntbara of fibers ooon in the moro peripheral air epooos. Furthor explanation ie roquirod to olarify this observation. Hate of T1asuo Reaction to Asbostos Fibers. The tiseuo reaction to asbestos develops much more rapidly than dooa tho reaction to quarts dust. S. Killer, William 3.i Tho Lung. Charles C, Thomas, Publishers, 1937. \ -6-