Document 4JBqRLaejb0Gx20bN9a8NJXdG

ASBESTOS 21S there was 1 milligram per gramme of nickel in the long even 8 years after cessation of exposure. If Loken's results were correct, there must have been some 1-2 grammes of nickel in the lungs--a wellnigh incredible figure-- completely out of harmony with Bames and Denz's conception of nonretention unless there was very great difference, as seems likely, in the physical form and states of the nickel. ASBESTOS The association of what appears to be purely mechanical trauma with a later development of neoplastic change has a long history both in the ex perience of myriads of medical observers and in thai of theorists who invoked it in the exposition of a theory of cancer. If such an association is looked at askance it is not because it is denied that it can occur, but rather that it is loo facile and even sterile an explanation. Of the tens of millions of mechanical traumas occurring daily, the number which can be later recognized as having possibly initiated a neoplastic process in situ is minute. Most pathologists would sum the matter up by saying that if trauma is followed by the develop ment of a tumour at the site of the original trauma, then that site was not normal at the outset. Co-carclnogenesis Tho classical experimental basis for the effect of the super-imposition of trauma on an abnormal site is the Deelman phenomenon, Deelraan showed in 1923 that if a tarred area of animal skin Is injured by wounding or other physical effect, tumour formation might be hastened and its location thereby determined. This observation was later confirmed by other workers who used pure carcinogens and laid the foundation of what is now called co carcinogenesis. Co-carcinogenesis may be defined as the augmentation of the action of a carcinogen by some suitable additional treatment which shows itself in increased numbers of induced lumours and/or shortening of tho induction time. In general the term co-carcinogenesis is applied to an effect produced by local application of an agent to a tissue (Borcnblum, 1947). A co-carcinogen is not itself a carcinogen although Anderson (1948) appears to think otherwise, regarding co-carcinogene$is as a synergy between sub liminal doses of two or more curemogens. Such mechanical irritation as strongly brushing the skin, and foreign body fibrosis, have been shown to be effective as co-carcinogens, heat, cold, radioactive radiations, croton oil and resin, all possess co-carcinogenic power. The precise nature of co-carcmogenesis is difficult to understand except as an expression of certain experimental facts. The significant matter from our present viewpoint is that Tor a co-carcmogcn to produce its effects it must be applied after a preparation of the tissue has taken place by a carci nogen, or even after an overt carcinogenic response has regressed. Although the whole conception of co-carcinogcnesis has arisen from