Document QgGpza8JJLoqN543RBqDQvJvo

1-23-2006 07: IS3 FR0|1: TO: 1618259^96 222 INDUSTRIAL CARCINOGENESIS AND lOXIOOLOOY inhalation, intratracheal insufflation, intravenously or intr&pcritonc&lly, Vorwuld, Durkan and Pratt (1951) recall that ordinary industrial (asbestos) dust apd, especially, long fibre asbestos dust from which (he small fibres had been separated, produced characteristic peribronchiolar fibrosis which remained static on discontinuance of exposure, whereas to particles of 3 n and lep there was no tissue reaction (King, Clegg and Rae, 1946). On substituting Brucilc (native magnesium hydroxide containing only 0-9 per ccit silica as silicate--Brucile is a crystalline compound easily split into tb n sheets and has a flexibility comparable to that of asbestos fibre), for the asbestos peribronchiolar fibrosis is similarly established, but dust of glass fit rc which is not flexible and, of course, cannot be split docs not, on long imal&tlon, lead to fibrosis. The dependence of the fibrosis on physical form was, however, settled by th s failure to induce fibrosis by long inhalation of asbestos which, having been fused and ground, no longer retained its original structure. The {Gardner school held that the combination of size, physical form and in mobilization in a rhythmically moving organ is the determinant of the pa ihogcnic effect. Effects somewhat similar to this pulmonary fibrosis can be obtained by iqjection of asbestos fibres into the peritoneum. But jat no stage in all these impressive researches was any clue obtained wi tich 'might have offered any support to the possibility that asbestos could ac t as a carcinogen. There is no reliable criterion by which one can anticipate carcinogenicity and, as is well known, relatively minute changes in the structure of a chemical carcinogen are sufficient to diminish or eliminate ca reinogeme action. If apbestos is indeed to be regarded as a carcinogen, tho need is felt to demonstrate some property which can be regarded as something more than inprtnps. The simplest such property Is solubility. Solubility confers some activity on a compound as, for example, in -the case of silica, the solubility ol' which in aqueous conditions is sufficient to found a chemical theory of si icosis. Asbestos has, however, not given much evidence of a solubility which night be significant. In analysing the working environment for asbestos dust Sundius and Bygden (1938) made the curious remark that only amphibole asbestos could be recognized in their analyses, in spite of the fact that the asbestos commonly used in indusiry contains mainly chrysolite und to a considerably lesser extent amphibole asbestos. This statement, if confirmed, might mean that chrysotile Is dissolved in the analytical process. In fact, chrysolite is the least resistant of asbestos types to chemical and physical agents' it is decomposed by hydrochloric and sulphuric acids, it loses water at red heat and its fibres can be fused in the bunsen flame. (Crocidolilo--blue asbestos--is also fusible to a black magnetic glass but is resistant to chemical agents). I Assuming that chrysotile might be capable of exerting some chemical P:11'13 effect by vir to the ashes have some: structure ir experiment: bodies did Cooke ( made the f spicules up soluble fra salt, have alveoli In recent Ife* in the elec that Cham the aetiolo Electron m The pro the electro the photo Cbampe Alkalii 10 minut Homo . cautiousl Decan iff To exs V* . To exi micro-m 'of the ol fracture As rega j-microscoj yith the iways > jpiyo<eprlocspseio ^fusiform < - Two ol ip. fibres _ collo iSnipula sLwereh.< iiese