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Lung tumours are not common in domestic animals; there has not been the increase in epidermoid carcinomas and anaplastic small-cell carcinomas that has occurred in man this century. Adenocarcinoma is the most common type in animals. The biological behaviour of each type of tumour in animals seems to be much the same as in man. The tumours are described histologically, the main categories being: epidermoid carcinoma, anaplastic carcinoma, adenocarcinoma, combined epidermoid and adenocarcinoma, carcinoid tumours, bronchial gland tumours, benign tumours, and sarcomas.

This classification is presented in two parts: (a) tumours of the gastrointestinal tract; and (b) tumours of the anal canal and margin. In the gastrointestinal tract the tumours are classified as adenoma, adenocarcinoma, and undifferentiated carcinoma, with several subtypes. Most polyps prove to be non-neoplastic, hyperplastic, or regenerative rather than adenomatous. Carcinoma of the stomach occurs mainly in dogs, but is a rare tumour in all parts of the world. Moderately differentiated, tubular adenocarcinoma of the small intestine with excessive fibrosis occurs in all six species; in some geographical locations it may occur frequently in sheep and cattle. The adenoma/carcinoma sequence in the rectum of the dog is similar to that in man but is encountered less often. Carcinoid tumours are very rare in domestic animals. Among the soft tissue tumours, those of smooth muscle and adipose tissue are found fairly frequently and congenital mesothelioma in the peritoneum of calves occurs occasionally. Tumours of the haematopoietic and related tissues are the most common gastrointestinal neoplasms in all species and most belong to the lymphosarcoma group. Tumours of the anal canal and margin are common in the dog and 90% of these are tumours of the hepatoid (perianal) glands.

A HISTOLOGICAL survey of lymphosarcoma1 (leukaemia) in 1968 in abattoirs throughout Great Britain showed an incidence of twenty-five cases per million pigs slaughtered, that is, ninety-two cases from 3.7 million pigs. There was multicentric lymphosarcoma in fifty-seven pigs and thymic lymphosarcoma in thirty-five pigs, and there was no indication of lymphosarcoma in other pigs on the farms concerned or even that it had occurred there previously. It is therefore of some interest that we have now found lymphosarcoma to have occurred several times in a single herd.

THE granular basophil cell of the tissues, the mast cell, has for long been thought to be the source of heparin1. Recently, it has been shown that the mast cell is also rich in histamine, a suggestion first made on histological grounds2 and afterwards confirmed by the finding of a strong positive correlation for mast cells and histamine in a wide variety of normal and pathological tissues3. However, up to the present, the only comparative study of mast cells for heparin and histamine in the same starting material has been carried out on normal ox lung, in which the pleura especially yielded high values for all three4. It is thus of some interest that we have recently obtained six cases of subcutaneous mast cell tumour from dogs for estimation of their heparin and histamine contents.