130 LEONELL C. STRONG 



number of operated individuals that continue to grow the tumor 

 progressively is approximately the same as those in the control 

 series that showed transitory masses only. The primary effect of 

 gonadectomy therefore lies in the fact that the source of origin 

 (gonads) of certain physiological checks inhibiting the develop- 

 ment of the tumor mass in normal non-susceptible individuals 

 has been removed. An individual of the non-susceptible race 

 is non-susceptible because it possesses physiological characteris- 

 tics that inhibit progressive growth on the part of the tumor 

 implant. 



This result suggests very strongly that the internal secretions 

 from the gonads somehow or other produce some of the physio- 

 logical checks referred to above. As above stated, tumor sus- 

 ceptibility is correlated with the phenomenon of assumption of 

 tissue specificity. The gonads are probably one of the most 

 important agents in bringing about these processes. A non- 

 susceptible strain is non-susceptible because the highly specific 

 physiological condition of adult individuals of that strain produces 

 a soil unfavorable for tumor implantation. Bj^ removing the 

 gonads we can prevent, to some extent, this process of assuming 

 high degree of specificity of the tissues. Very young individuals 

 of a non-susceptible race are sometimes susceptible to implanted 

 tissue, although no adult individual of the same race will grow 

 the tumor. Gonadectomy therefore allows the progressive 

 growth of certain of those tumor masses that would have re- 

 gressed in a normal (non-susceptible) individual. 



A most interesting result was obtained by comparing the age- 

 susceptibility curve for gonadectomized individuals with that 

 for the controls (fig. 27, p. 111). Several very striking results 

 w^ere obtained. It will be noticed that the two curves are en- 

 tirely different. 



We started out with the idea that the younger the mice 

 employed for operation, the more effect the removal of the 

 gonads would probably have, due to the fact that differentiation 

 would never have the opportunity to proceed as far as in normal 

 individuals. This is not the case, however. If very young 

 individuals are gonadectomized, no apparent reaction masses 

 of the implanted tumor can be detected, no matter how many 



