Possible Biological Importance of Fibre Diameters of South African Amphiboles

IN the preceding communication, Harington, Gilson and Wagner1 comment on the need to explain the big difference in the number of mesotheliomas reported from the crocidolite mining area of the north-western Cape compared with that in the Transvaal where both crocidolite and amosite are mined. Although the experimental results they quote can be accepted as evidence on the relative carcinogenicity of the various types of asbestos, the intra-pleural inoculation method used to introduce these materials does not take account of the natural factors involved when the fibres are inhaled.