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Asbestosis and Allied Diseases

gas transfer in the lung and which causes progressive restriction of ventilatory capacity. Impairment of gas transfer can be detected before there are any radiological changes indicating fibrosis. Fortunately, as a result of improvement in occupational hygiene following the implementation of legislation, this disease is becoming rare. The development of fibrous plaques which may subsequently calcify is dealt with in detail in the accompanying papers. Among workers exposed over several years to asbestos of any type lung cancer is found more frequently than among the general population (Doll 1965), though the excess is happily diminishing (Knox et al. 1968). Selikoff et al. (1969) have pointed out that lung cancer is only found in asbestos workers who also smoke; this may be true synergism in the mechanism whereby these cancers are produced. The study of Wagner et al. (1960), describing the associations between pleural mesothelioma and exposure to crocidolite, began a new era in work on asbestos since they demonstrated that the exposure to the dust which produced these fatal tumours could be acquired merely by living near to mines or works processing crocidolite. The prevalence and distribution of these tumours have been studied by many workers in this country and a similar association with occupation or residence near asbestos works has been demonstrated (Newhouse & Thompson 1965). Exposure need be only minute and the tumours may not appear for forty years. There is evidence which leads one to suggest that peritoneal mesotheliomas may, too, be associated with exposure to asbestos and there have been reports of higher incidences of cancer of the gastrointestinal tract among asbestos workers (Hammond et al. 1965). The asbestos body merits mention. It is an odd dumb-bell-shaped microscopic body consisting of a fibre enclosed in a proteinaceous sheath stained with ferritin, is found in sputum and in the lung and signifies merely that the subject has at one time been exposed to asbestos and not that he is suffering from asbestosis. When sought diligently in post-mortem material it has been shown that the lungs of most of us, even in the absence of occupational exposure, contain asbestos bodies. There has been some recent work which suggests that not all the bodies which used to be thought to be asbestos bodies do indeed contain asbestos fibres and that unless the mineral is identified with certainty by electron diffraction or the use of other techniques the bodies ought more properly to be termed 'ferruginous' (Utidjian et al. 1968). Much research is in progress to identify the carcinogen in asbestos. Polycyclic hydrocarbons have been detected and there are some paraffinlike fractions which can be extracted by prolonged refluxing with organic solvents. It is important to make sure that some of the organic material found in asbestos by several workers is not a contaminant. During the mining and milling processes there are many opportunities for contamination. During careful analyses of standard samples used in experimental work Commins & Gibbs (1969) found that one of the impurities was derived from an anti-oxidant incorporated in the polythene bag in which the samples were stored. Likewise some commercial samples may be contaminated by oil from the jute bags in which the asbestos is shipped. As research on the nature and effects of the various types of asbestos proceeds we would do well to heed Legge's aphorism: where possible use a safe substitute.