8 SCIENCE PROGRESS 



twenty sporadic mouse tumours, and conclusively proved that 

 the cancer cells are merely transplanted into the new animals 

 which provide them with nourishment, by means of a specific 

 connective tissue reaction supplied afresh after each fresh 

 transplantation. 



The criticism, that the tumours experimented with were not 

 comparable with cancer in the human subject, was advanced as 

 speedily as of yore, and with all the assurance born of a know- 

 ledge of its effectiveness in discrediting earlier experiments. It 

 is still feebly uttered by certain persons who lack extensive 

 experience of cancer in animals. At last, however, it was to be 

 met satisfactorily. Before proceeding to the study of other 

 problems, Murray and myself spent much time in demon- 

 strating, not only that the starting-point of the experiments 

 has been cancer of the mamma, but were at great pains to 

 reproduce artificially metastases, infiltrative and expansive 

 growth — in short, all the main features of the disease in previ- 

 ously healthy animals. With Cramer we drew a parallel 

 between the growth of cancer under natural and experimental 

 conditions. Haaland independently did the same for a number 

 of carcinomata, and demonstrated that Ehrlich's experimental 

 sarcoma formed metastases, and behaved in other ways like a 

 malignant new growth of the human subject. Apolant published 

 an elaborate and valuable monograph on the histology and 

 pathology of the mammary tumours of the mouse. 



These results are based on observations all but limited to the 

 mouse. As yet our numerous inoculations of cancer in other 

 vertebrates have met with only transitory success in rats and 

 in a single carcinoma mammae of the dog. Even in the case of 

 mice there are great difficulties to be overcome : for the other 

 vertebrates many of the difficulties are still unsurmounted. The 

 failures may be due largely to the relatively small number of 

 inoculations made as contrasted with mice, as well as to 

 difficulties associated with varying suitability of the animals 

 employed, which the study of the transplantation of cancer in 

 mice has proved is a factor of great importance. 



The inoculation of cancer in mice has been necessary on 

 a scale perhaps unprecedented in the experimental study of 

 disease, in order to prove that the cancer cell is able to grow 

 and to proliferate continuously in animals of the same species 

 only. To establish that the cancer cell is not transferred 



