THE STUDY OF CANCER 9 



naturally from one individual to another, equally extensive 

 observations have been necessary. As I shall show later, the 

 cancer cell of the mouse is in all probability a mouse cell 

 incapable of nourishing itself and proliferating, except when 

 in intimate organic union with the body, and nutrient supply, 

 of the living mouse. Ehrlich has shown that a transitory growth 

 follows the transplantation of one of his mouse tumours into 

 rats. We found that the same power is possessed by other 

 mouse tumours. Growth, however, speedily ceases in rats, 

 although it is retained unimpaired if the cells be re-transferred 

 to mice after a short sojourn of six to eight days in the rat's 

 body. A mouse tumour does not grow equally well in all mice. 

 We found difficulty at first in getting Jensen's Danish tumour 

 to grow in English mice, and Michaelis and others have entirely 

 failed to get it to grow in the mice of Germany, England, and 

 other countries. 



The progress made by the demonstration, that cancer could 

 be transplanted and artificially propagated ad libitum, was not 

 of the obvious kind appealing to the multitude. If transference 

 had proved that the tissues of the new animal acquired cancerous 

 properties, i.e. that the disease could be conveyed by way of 

 infection, our knowledge of its nature would have been advanced 

 enormously at one step. Then investigation could have been 

 legitimately limited at once to identification of the agent and 

 of the channels of infection. 



The nature of the transference of cancer was out of accord 

 with all known processes of infection, in this respect merely 

 presenting old problems in a new light, as well as new problems 

 for solution. However, Murray and myself were able to draw 

 certain conclusions other than those drawn by Jensen, which 

 have been abundantly confirmed since by others : (1). The 

 amount of proliferation exhibited is enormous, once the primary 

 difficulty of transplanting a mouse tumour at all has been 

 overcome. The proliferation is then out of all conformity with 

 the laws of growth in vertebrate organisms. The cancerous 

 tissue retains its histological characters. (2) If a large number 

 of healthy mice be considered, growth proceeds readily in mice 

 in which cancer is rare naturally. Although the maximum 

 incidence of cancer occurs in the later years of life, growth 

 proceeds as well, and even better, in young animals than in 

 old. Therefore, if senescence is intimately bound up with the 



