Structural variations between pleural and peritonea1 mesotheliomas produced in rats by the injection of crocidolite asbestos

The author studies the ultrastructure of pleural and peritoneal mesotheliomas caused in the rat by the intra-pleural or intra-peritoneal injection of 25 mg of crocidolite. In the peritoneum the tumour is made up chiefly of “connective” type tissue with rare “epithelial” cells. In the pleura, the “epithelial” cells predominate, constituting vast vegetating “papillomatous” zones or “adenomatous” territories. The author recalls Willis’ concept, and feels that mesothelial tumours in the rat, caused by asbestos, represent one aspect of the family of mesenchymatous tumours, with their ability to behave differently according to their site.