Azo-dyes and experimental liver tumours.

Introduction Several hundreds of cancer-producing chemical compounds are now known. By far the largest group, which contains all the very potent carcinogens, consists of compounds, mostly polycyclic aromatic hydrocarbons and simple derivatives of these, which give tumours at the site of application. Malignant tumours, resulting from prolonged contact of the tissues with the chemical compound, may be induced in many different tissues and organs. Repeated application to the skin gives epitheliomas, subcutaneous injection (in solution or in the solid state) gives tumours of connective tissue (sarcomas), and by suitable application cancer may be induced in the lung, mammary gland, liver, kidney, spleen, brain, prostate and uterus, and in bone and in other tissues also. Several different species are susceptible, e.g. rats, mice, guineapigs, rabbits, hamsters and fowls. Different species and different organs vary very widely in their response to a particular compound, and different compounds also show considerable variation in their action. These variations are, on the whole, quantitative rather than qualitative. Yet, while many derivatives of I :e-benzanthracene are equally effective in producing both skin tumours and subcutaneous tumours in mice, some of them give tumours more rapidly by the injection technique. On the other hand, derivatives of 3:4-benzphenanthrene have proved much more effective when applied to the skin (Badger, Cook, Hewett, Kennaway, Kennaway & Martin, 1942). All the evidence is consistent with the view that these polycyclic hydrocarbons act directly on the cells. A second group of compounds having cancer-producing properties comprises the oestrogenic substances, both natural and artificial. These compounds do not in general produce tumours at the site of application, but their administration by any route to female mice results in a large increase in the incidence of mammary carcinoma. It now * See notice on p. 306. 245