HEREDITY AND TRANSPLANTATION OF TUMORS 375 



retains some of the essential characteristics of thyroid tissue and is, therefore, 

 more susceptible to injurious influences. There is good reason for assuming 

 that different tissues, such as cartilage and thyroid, and cancers derived from 

 them which develop in the same host, possess the same genetic constitution 

 and the same individuality differential, and that differences which such tissues 

 and cancers show, are therefore, in all probability, directly non-genetic, al- 

 though ultimately they depend also on the constitution of the germinal gene 

 sets. (5) There are certain factors of an environmental nature which may 

 also, under some conditions, influence the number of successful transplanta- 

 tions. Severe undernourishment may diminish it ; hormones may affect the 

 transplantability. Thus according to the recent experiments of Gross, trans- 

 plantation of a mouse sarcoma succeeded more readily in sexually mature 

 male than in female mice. He could make it very probable that the ovary gives 

 off a substance, presumably a hormone, which had this inhibiting effect on the 

 growth of the transplanted tumor. This is of importance, because it has been 

 taken for granted by some investigators that slight differences in the effect of 

 sex on the number of takes observed at a certain time of life were of genetic 

 origin. However, it must be noted that Gross carried out intracutaneous trans- 

 plantations and that under these conditions the existence of the tumors is a 

 very labile and rather precarious one, in which slight interferences, which in 

 transplants growing under more favorable conditions would hardly be notice- 

 able, may affect quite definitely the fate of the tumor. The effect of the hor- 

 mone in this case is presumably an indirect one. (6) Other intrinsic factors 

 such as growth momentum, immunizing power, and adaptability of tissue to 

 the condition of the host, all of which are greater in tumors than in normal 

 tissues. 



As far as the growth momentum is concerned, its constant increase in 

 cancer tissue over that in the normal tissue from which it originated, is per- 

 haps the most characteristic feature of tumor tissue. This increase in growth 

 momentum makes it possible for cancer tissues to resist injurious influences 

 to which normal tissues would succumb, the rapid cell multiplication probably 

 increasing the ability of the transplant to absorb and neutralize injurious sub- 

 stances circulating in the host. Associated with this greater growth momentum 

 there is usually a diminution in differentiation of the cancerous cells, which 

 may likewise diminish the sensitiveness of the transplant to injurious factors 

 under certain circumstances. However, the growth momentum is not a sta- 

 tionary condition ; in a very large number of instances it has been observed 

 that during the first transplantations of a tumor, whether a carcinoma or a 

 sarcoma, the growth energy increases. Such an effect is typical, as we found 

 about forty years ago in the course of our first transplantations of sarcoma of 

 the thyroid gland in rats, and it has since been noted by many other investi- 

 gators. There is no justification for assuming that so regular an occurrence, 

 which does not depend upon a single tumor cell but may be noted after 

 transplantation of various parts of the tumor, is due to a haphazard somatic 

 mutation. It is presumably due to the stimulation exerted by incisions into the 

 tumor and by the process of transplantation. A similar stimulation has been 



