Document VjOKwvV9MR5Rz52BRrZv43xzj

8 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE Impinger samples taken soon after the experiment was started indicated that the dust concentration was at first quite low, the average dust count being only 6.0 million particles per cubic foot of air by the standard light field technic and 0.8 million for particles and fibers greater than 10 microns. After the inhalation experiment had been under way for about two years, the speed of the rotating paddle in the dusting machine was increased and for the remaining 10 months of the experi ment considerably more dust was dispersed into the atmosphere. The average dust count of impinger samples collected after this change was 53.7 million by the usual light field method and 1.6 million for particles and fibers larger than 10 microns. It is probable, however, that the true values of the dust concentration were higher than the counts given in this paragraph. The impinger samples for the King's floats experiment were collected in water, but later studies7 have shown that counts of impinger samples of asbestos dust taken in water are not reliable. Ethyl alcohol instead of water was used as the collecting fluid in all subsequent experi ments. Table 4.--Summary of Inhalation Experiment with King's Floats Asbestos Dust Nature of Experiment Dust exposure continuous throughout life Dust exposure followed by prolonged residence in normal air Tuberculous infection * at start of dust exposure Controls to infection: no dust exposure Tuberculous infection * after 28 mo. of dust exposure, then residence in normal air Controls to infection: no dust exposure Animals 54 guinea pigs 9 rabbits 18 rats 25 guinea pigs 25 guinea pigs 1 rabbit 1 rabbit 40 guinea pigs 23 guinea pigs 12 guinea pigs 12 guinea pigs Maximum Maxi- Survival mum' After Dust Ex- Dust Exposure. posure, Mo. Mo. 33 0 19 0 60 6 35 9 37 6 30 ) 19 34 J 35 0 0 35 t Results Typical peribronchiolar fibrosis after 16 months Foreign body bronchitis Little or no reaction Nonprogressive fibrosis Nonprogressive fibrosis Absorption of foreign body reaction Temporary progression of infection, followed by healing with fibrosis Healing by resolution (one exception) 26 14 No appreciable increase in susceptibility to tuberculous infection; healing with fibrosis 0 19 t Healing by resolution * The guinea pigs were Infected with low virulence Ri strain of tubercle bacillus, t This means the survival period following infection. Results of the investigation, briefly summarized in table 4, show that inhalation of King's floats asbestos dust produced a typical peribronchiolar fibrosis in guinea pigs but not in rabbits or rats. Reaction in Normal Guinea Pigs.--Guinea pigs inhaling this dust for periods up to 33 months had a characteristic fibrosis occurring in conical patches about the respiratory bronchioles. During this exposure the peripheral alveoli were not involved. The particulate elements of the dust were transported through the lymphatic system to the bronchial nodes, causing no significant reaction in either site; the fibrous elements remained fixed at the points of original localization and were seldom detected in the lymph nodes. After exposure of approximately a year a small amount of cellular reaction had been produced about many respiratory bronchioles (fig. 3 A). As more dust was inhaled, it continued to accumulate in the same location, and later stages of the disease (fig. ZB) consisted of extensions of the original lesions. Apparently, the inhaled fibers were caught in the pocket-like alveoli that are given off from the lateral walls of the respiratory bronchioles. There they 7. Fulton, W. B.; Houtz, R. L.; Dooley, A., and Mathews, J. L.: Asbestosis: I. The-Collection and Counting of Asbestos Dust Encountered in Asbestos Fabri cating Plants, Special Bulletin 37, Pennsylvania Department of Labor and Industry, Harrisburg, 1934.