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352 DAVIS AND CONIAM that whereas intrapleural injection of asbestos in rats produces large numbers ot mesotheliomas (Wagner, 1960) few are produced by similar injection in mice (Davis, unpublished) and so no significant results would have been produced from prolonged experiments of this type using brake lining dust. It is planned to undertake new series of experiments that will test the long-term effects of brake lining dust in conditions where normal chrysotile is known to produce tumors. At this point, however, it may be pointed out that electron microscope studies of lesions produced in response to brake lining dust have shown that this dust contains extremely little recognizable chrysotile and what there is is mostly embedded in the plastic bonding material. No computation of urban atmospheric pollution by chrysotile from this source can therefore be made by calculating brake drum wear. REFERENCES Allison, A. C., Harincton, J. S. Birbeck, M., and Nash, T. (1985). Observations on me cytotoxic action of silica on macrophages. Inhaled Particles and Vapours, II. In "Proceedings of the British Occupational Hygiene Society Symposium, Cambridge" (Davies, C. N., ed.), pp. 121-131. Published by Pergamon Press. Anjilvel, L., and Thurlbeck, W. M. (1966). The incidence of asbestos bodies in the lungs at random necropsies in Montreal. Can. Med. Atso. J. 95, 1179-1182. Ball, M. C., and Taylob, H. F. W. (1963). The dehydration of chrysotile in air and under hydrothermal conditions. Mineralog. Mag. 33, 467-482. Brindley, G. W., and Hayami, R. (1965). Mechanism of formation of forsterite and enstatite from serpentine. Mineralog. Mag. 35, 189-195, Catjna, D., Totten, R. S., and Gross, P. (1965). Asbestos bodies in human lungs at autopsy. JAMA 192. 371-373. Dale, J. C., and Kino, E. J. (1953). Acute toxicity of mineral dusts. AMA Arch. Industr. Hyg. Occup. Med. 7, 478-483. Davis, J. M. G. (1968). The effects of chrysotile asbestos dust on lung macrophages main tained in organ culture. Brit. /. Exp. Pathol. 48, 379-385. Davis, J. M. G. (1970a). The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals. Brit. J. Exp. Pathol. 51, 617-627. Davis, J. M. G. (1970b). Further observations on the ultrastructure and chemistry of the formation of asbestos bodies. Exp. Mol. Pathol. 13, 346-358. Davis, J. M. G. (1972). The fibrogenic effects of mineral dusts injected into the pleural cavity of mice. Brit. J. Exp. Pathol. S3, 190-201. Davis, J. M. G., Gross, P., and De Trevelle, R. T. P. (1970). Ferruginous bodies in guinea pigs. Arch. Pathol. 89, 364-373. Ericsson, J. L. E., and Trump, B. F. (1964). Electron microscopic studies of the epithelium of the proximal tubule of the rat kidney. Lab, Invest. 18, 1427-1456. Gye, W. E., and Purdy, W. J. (1924), Poisonous properties of colloidal silica. Brit. J. Exi>, Pathol 5, 238-250. Heppleston, A. G. (1967). Activity of a macrophage factor in collagen formation by silica. Nature (London) 214, 521-522. Jacatic, J., Rubnitz, M. E., Godwin, M. C., and Weiskopf, R. W. (1967), Tissue response to intraperitoneal asbestos with preliminary report of acute toxicity of heat treated asbestos in mice. Environ. Res. 1, 217-230. Kino, E. J., Clecg, J. W., and Rae, V. M. (1946). Effect of asbestos, and of asbestos and aluminum on the lungs of rabbits. Thorax 1, 188-197. Klosterxotter, W., and Jotten, K. W. (1953). Die Wirkung Verschiedener Kiesselsaureforinen in Tierexperiment. Arch. Hyg. 137, 625-636.