1909.] The Incidence of Cancer in Mice of Known Age. 



313 



disease, the theses which have found such ready acceptance must be regarded 

 as not proven. 



As in the case of other communities of mice in outside breeding establish- 

 ments, our stock, at present under consideration, is a highly in-bred one. It 

 is not profitable at present, considering the small number of tumours which 

 have been obtained, to analyse the cancerous and non-cancerous individuals 

 with reference to this factor or to the ancestry. 



The positive value of these observations lies in the statistical confirmation 

 they bring to the results of the comparative histological and biological studies 

 of the Imperial Cancer Research Fund, which have shown the close parallel, 

 amounting in many particulars to complete identity between malignant 

 new growths in man and other vertebrates. They demonstrate that the law 

 of the age-incidence of cancer holds also for the shortest-lived mammals as it 

 holds for man. Since the facts accord with the imperfect data we have 

 elicited for other vertebrates, they make the general applicability of the law 

 of age-incidence probable, and therefore any explanation of the etiology of 

 cancer must accord with the circumstance that, when considered statistically, 

 cancer is a function of age, and when considered biologically is a function of 

 senescence. 



VOL. lxxxi. — s, 



Z 



