118 LEONELL C. STRONG 



are supposed to be endowed with different capacities for adap- 

 tation. He admits, however, that prohferative energy may be 

 a secondary factor. From the genetic viewpoint, several ob- 

 jections appear to be vahd: 1) all the results which he obtained 

 are supposed to be explained by adaptive characteristics of the 

 tumor cell alone; 2) ''mice from the same source" introduce a third 

 variable; this, however, he does not take sufficiently into con- 

 sideration; 3) the supposedly fluctuating power of adaptation on 

 the part of the tumor cell appears up to the present time to have 

 been based upon the old conception of the inheritance of acquired 

 characteristics and is therefore unsupported by experimental 

 evidence. 



In our own experiment we found that identical histological 

 adenocarcinomas (derived from two very closely related individ- 

 uals) possess different physiological reactions when placed into 

 the same mice (not individuals derived from one dealer). Our 

 last experiment (outlined in fig. 33) demonstrated that in these 

 tumors, at least, there was no power of adaptation present. 

 Evidently another explanation is therefore necessary. 



"It is of course true that cells which are not morphologically 

 different in any visible way may show themselves by their behavior 

 to be physiologically different, so that the absence of visible 

 differentiation in the cell is not proof that the cell is completely 

 unsJDecialized" (Child, Senescence and Rejuvenescence, p. 48). 



We have some evidence to show that the two apparently 

 histologically identical tumor cells differ from one another in 

 one or more mendelian units. (This point can only be tested 

 by raising an Fo generation between a susceptible and a non- 

 susceptible race. This experiment is now in progress. The 

 numbers obtained so far are not yet large enough, however, to 

 give conclusive proof for this contention.)^ The two tumors 

 have different characteristics: 1) They possess different reac- 

 tion potentiahties and, 2) they differ in their genetic constitu- 

 tion. Are we justified in drawing the conclusion that the dif- 

 ference in their reaction capacities within a non-susceptible race 



' Thus we find that some F2 animals grow both tumors, some one or the other, 

 and some neither, indicating a genetic difference in the tumors, the underlying 

 elements of which are segregating. 



