126 LEONELL C. STRONG 



suppose that certain tumors should show a differential reaction 

 between the sexes for adult mice also. Certain tumors must be 

 differently affected by sex hormones, and other internal condi- 

 tions characteristic of one or the other sex. The neoplasms 

 that have given rise to transplantable tumors are decidedly 

 more prevalent in females than in males. For that reason, 

 primarily, they probably, in some cases, vary from those arising 

 from male tissue. 



The dBrA tumor used in this experiment appears to be slug- 

 gish. When it is grown together with the dBrB in the same in- 

 dividual of a highly susceptible race (either an Fi or a first back- 

 cross animal), it is always handicapped by the greater growth 

 vigor of the dBrB mass. Because of its sluggishness, primarily, 

 we believe that it was unable to show a differential effect of sex 

 (as did the dBrB tumor) when all age groups were massed. One 

 point of importance need be emphasized — when the dBrA tumor 

 underwent the probable mutational process in the experiment 

 N, previously referred to, it not only approached the greater 

 reactive potentiality of the dBrB tumor, but also showed a 

 similar differential effect upon the sexes (fig. 14). In fact, it 

 not only exceeded the dBrB tumor in vigor of growth, but also 

 produced a differential effect upon the sexes when only adult 

 individuals are considered (fig. 15). This result can be explained 

 on the assumption that the increased activity of the dBrA tumor 

 was so great that it could even differentiate between the slight 

 metabolic differences in adult mice. 



To sum up the factor of sex underlying susceptibility to trans- 

 plantable tumors, we may say: 1) That the influence of sex is 

 probably a secondary phenomenon of the age factor. 2) That 

 the role of sex in determining susceptibility or non-susceptibility 

 may also have some relation to the attainment of physiological 

 specificity of the tissues. 3) That the inherent capacities of 

 the tumor cell itself may determine to some extent the degree 

 of influence which sex has on the fate of the implant. 



