The incidence of cancer in mice of known age

The opportunity of obtaining accurate information of the frequency of spontaneous cancer in mice at different age-period has presented itself in the course of a prolonged inquiry into the possibility of hereditary transmission of a liability to cancer. We have approached the question of heredity experimentally by breeding systematically from mice spontaneously affected with malignant new growths, and propose to determine the frequency of spontaneous cancer in mice in whose ancestry the disease has occurred with varying frequency. This investigation is still in progress and cannot be reviewed profitably for several years, but the data which have so far accumulated are of sufficient interest, in their bearing upon the statistical and biological importance of the age-incident of the disease, to warrant a preliminary account being published ; although the small numbers at present available still render the greatest caution necessary. The method by which the data have been obtained is as follows : Mice spontaneously affected with cancer are not killed when brought into the laboratory, but the tumors are excised and used for translation. The clinical course, the microscopical examination and the results of transplantation. The clinical course, the microscopical examination, and the result of transplantation of the tumours, together withpost-mortem examination of the animals, give the best security for the correctness of the diagnosis of cancer. It is only under these precautions that the breeding experiments have proceeded. Each spontaneously affected mouse, or pair mated for breeding, has been housed in a separate cage. The cages have been sterilised and changed at regular intervals. In the first instance, the males mated with these spontaneously affected animals received pregnant. Later, males bred in the laboratory from cancerous parents were used, so that the pedigrees constructed for the later litters show some strains with a relatively enormous preponderance or cancerous ancestors. When a little is born each young mouse receives a number, the date of birth is entered in a list, and the sex and colour or other distinguishing marks noted against each. So soon as they are able to look after themselves the litters are separated from the mother, and the males and females segregated in fresh cages. It is thus possible to distinguish each animal born in the laboratory by reference to an index, which at once gives the ancestry, the date of birth, and the age of the animal in question. The mice have been systematically examined daily.