310 



Hie Incidence of Cancer in Mice of Known Age. 



By E. F. Bashford, M.D., and J. A. Murray, M.D., B.Sc, Imperial Cancer 



Kesearch Fund. 



(Communicated by Prof. J. Rose Bradford, Sec. R.S. Received April 30, — 



Read May 20, 1909.) 



The opportunity of obtaining accurate information of the frequency of 

 spontaneous cancer in mice at different age-periods has presented itself 

 in the course of a prolonged inquiry into the possibility of hereditary trans- 

 mission 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 

 loe 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-incidence 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 labora- 

 tory, but the tumours are excised and used for transplantation. The clinical 

 •course, the microscopical examination, and the results of transplantation of the 

 tumours, together with the post-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 females were the offspring of 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 of cancerous ancestors. When 

 a litter 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 



