HEREDITY AND TRANSPLANTATION OF TUMORS 373 



servations of Strong without having recourse to the assumption of different 

 genetic mutations in different somatic cells of the same individual. 



However, there are certain other conditions which may correctly be at- 

 tributed to genetic conditions. Thus Strong and Bittner observed in the course 

 of their transplantations that in the closely inbred strain, "dilute brown," 

 a change suddenly took place in the transplantability of a certain tumor and 

 they attributed this change to a selection within the larger strain of a certain 

 substrain or family, which thus evidently differed in genetic composition 

 from that of the main strain. This agrees with our previous observations, 

 in which we had found a similar change in the transplantability of tumors and 

 also in the percentage of spontaneous tumors developing in a strain of mice, 

 due to the splitting off of certain families possessing a somewhat different 

 genetic composition. 



From our findings after transplantations of normal tissues and of several 

 tumors, we concluded that in a general way the outcome of transplantation 

 depends upon the relation between the organismal differentials of host and 

 transplant; and this means that it depends, essentially, upon the genetic con- 

 stitution of the tumor cells as well as of the host cells, and that the reaction of 

 the latter takes place in response to the strange genes carried by the transplant. 

 In the strict sense the reaction does not, however, occur against the genes as 

 such, but against certain physiological and biochemical mechanisms developing 

 in transplant and host on a genetic basis. Strong expressed more recently the 

 same idea that the result of tumor transplantation is a function of the genetic 

 composition of both host and transplant. In this respect, then, the various 

 investigators are in agreement. 



There still remains to be discussed the relation between the hereditary pre- 

 disposition to cancer and the change which takes place in normal cells during 

 their transformation into cancer cells. These two conditions are distinct from 

 each other. A comparison between the transplantation of normal tissues and 

 of tumors which arise from normal tissues makes possible an analysis of the 

 constitution of the individuality differentials of both, and we studied tumor 

 transplantation largely from this point of view. Tyzzer, on the other hand, 

 in common with Ehrlich, and also to some extent in common with Bashford, 

 considered tumors as essentially different from ordinary tissues, as an abnormal 

 condition which called forth an immunity peculiar to cancer, although certain 

 exceptions to this rule were admitted. Thus Tyzzer assumed that the genetic 

 study underlying transplantation of tumors might furnish an insight into the 

 character of cancer and into the conditions which cause its development. Simi- 

 larly, Little, Strong and Bittner infer a similar connection between the 

 hereditary factors determining transplantability of tumors and the origin of 

 tumors, and in this sense, Bittner intimates that the same dominant multiple 

 factors which determine the transplantability of tumors may determine, also, 

 the origin of cancer. 



We shall now attempt to analyse still further the various data which we 

 have discussed, and to determine, if possible, the significance of genes in the 

 transplantation of tumors. For this purpose it will first be necessary to consider 



