HEREDITY AND TRANSPLANTATION OF TUMORS 371 



several spontaneous sarcomata which developed in the thyroids of different 

 rats, differed very much in their behavior after inoculation into other rats, 

 although these tumors were very much alike in their structure. 



Continuing these experiments, Strong, as well as Bittner, studied two 

 tumors which developed spontaneously in the same mouse of an inbred 

 strain. These two tumors likewise were found to behave differently after 

 transplantation into the same and into other inbred strains and into differ- 

 ent generations of hybrids, and it was therefore believed that they differed in 

 the number of genetic factors required for their continued growth in a strange 

 host. Also, Cloudman, who transplanted three tumors originating in a mouse 

 of the inbred A strain, and Bittner, who compared the growth of multiple 

 tumors which developed spontaneously in an F x hybrid between the A and D 

 strains, obtained similar results when the individual tumors were transplanted 

 into A and D strains and into the different hybrid generations between A and 

 D. But, although one of Strong's tumors grew in a larger number of individ- 

 uals belonging to another strain and in hybrids between its own and the strange 

 strains, otherwise the two tumors behaved in a parallel way as far as the rela- 

 tive percentages of their takes in these different kinds of mice were con- 

 cerned. Both tumors were also affected in the same way by sex differences of 

 the hosts after transplantation into F x ^hybrids, the females being the more 

 favorable hosts. 



Previously, Little had assumed that in female mice at the time of sexual 

 maturity a change in the receptiveness to transplants occurs. He attributed the 

 difference which he observed in the percentage of takes in newborn female 

 mice and in mice three weeks old, to the sexual maturity which takes place 

 during this period and to corresponding changes in the individuality differ- 

 entials ; this would represent a linkage between susceptibility and sex factors. 

 But only in certain hybrid strains did the number of takes increase at the time 

 of sexual maturity, while in the white and dilute brown parent-strains the re- 

 verse relation was noted. Furthermore, the differences between these age 

 classes with which Little dealt were only slight. 



More recently Bittner described another case of what he interpreted as 

 linkage, namely, one between the factors determining transplantability of a 

 certain tumor and the color of the skin ; but in this case also, the differences 

 in the percentage of takes in different groups of white mice differing in their 

 hair color were slight. As to the effect of sex on transplantability of tumors, it 

 is conceivable that sex hormones may, under exceptional conditions, favor the 

 growth of certain mammary gland carcinomata in the same way as, in accord- 

 ance with our previous observations, they may do in benign tumors of the 

 mammary gland; however, such an action is not likely to affect fully devel- 

 oped carcinomas ; they no longer respond, as a rule, to hormones. We, as well 

 as Strong, Cloudman and Bittner, assumed that differences in the percentages 

 of takes of tumors originating in the same animal, in hosts with a similar 

 genetic constitution, depend upon differences in the characteristics of these 

 tumors, but we do not agree in our interpretation as to the nature of such 

 differences. 



