124 LEONELL C. STRONG 



One conclusion (no. 9) was reached by Little that is of primary 

 importance to our own investigation: ". . . . females of 

 the upper age group in both series are, during the later periods 

 of observation, at an age when sexual maturity is attained. Sexual 

 maturity by the awakening activity of the ovary means further 

 differentiation and further development of individualit}^ of the 

 tissue. Such assumption of individuaUty leads to elimination 

 of the tumor in non-susceptible animals and to encouragement 

 of its growth in animals inheriting all or parts of the factors 

 which are contributed by, and which characterize susceptible 

 animals of the Japanese waltzing race in which the tumor 

 originated." 



In our own experiment we were able to verify the previous 

 conclusion of Little and to continue the study to include all age 

 groups. The interesting fact was determined that there is no 

 significant difference for adult mice between the sexes in sus- 

 ceptibility to transplantable tumors, whereas when all age groups 

 are massed there is a significant difference. In other words, 

 we are confronted with the fact that young males give a greater 

 number of visible reactions than do young females, although the 

 sexes are very uniform in their reactions to a foreign tissue when 

 only adult mice are considered. 



Age is, perhaps, the most important factor underlying 

 susceptibility to transplantable tumors. Can we explain this 

 observed sex difference by the age factors? It has long been 

 recognized that female mice mature faster than their Utter 

 brothers. Wlien the tissues of the female affected by the secre- 

 tions of the gonads have commenced to attain their adult speci- 

 ficity due to the approach of sexual maturitj^, the male of similar 

 age is distinctly more inmiature. Little recognized the fact 

 that with approaching maturity, susceptibility toward trans- 

 plantable tumors for a non-susceptible strain rapidly decreases. 

 The elimination of the tumor is perhaps correlated with the dif- 

 ferentiation of the tissues depending upon several functioning 

 elements, one of which is the gonads. This suggests that the 

 young females are less susceptible to the tumor reaction because 

 they are maturing (growing older) faster than the males. When 



