SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 119 



somehow or other correlated with the genetic difference which 

 the tumors themselves show? 



2. Fluctuations in 'groivtli' energy or 'adaptation^ 



That tumor cells fluctuate remarkably in their rate of pro- 

 liferation is commonly acknowledged. Such changes, however, 

 are not always uniform (either increasing or decreasing), as 

 might be expected if the tumor cells underwent rhythmical 

 activities. The sudden appearance of an increased activity on 

 the part of the tumor cells cannot be explained by assuming that 

 the cells possessed the capacity of adaptation for any particular 

 host. If this is the case, we have given both tumors ample 

 opportunity to express their inherent potentiality. With one 

 exception, neither tumor ever grew progressively in a normal 

 wild mouse, although hundreds have been inoculated. 'Adapta- 

 tion' certainly ought to have expressed itself more than once 

 in that time. Again, absence of proliferative energy alone can- 

 not be the cause for the failure of the wild mice to harbor the 

 tumor tissue. Individuals from a susceptible strain of mice were 

 inoculated periodically throughout the experiment and they 

 grew both tumors in 100 per cent of all inoculations. The one 

 exception among the wild mice occurred in an adult male indi- 

 vidual, no. W238. For some unknown reason, this mouse alone 

 of all the controls inoculated grew the dBrA tumor progressively.^ 

 The same tissue that was employed for W238 was also inoculated 

 into several other individuals. This single experiment (fig. 3) 

 gave more percentage reactions for this 'exceptional' dBrA 

 tumor than for all the other experiments dealing with the dBrA 

 tumor combined. The mice are probably of the same general 

 genetic constitution as those used in all other experiments with 

 wild mice (discussed on page 76). The progressively growing 

 tumor (derived from W238) was inoculated on both sides in the 

 inguinal region of thirty other wild mice. Not one of the mice 

 ever showed a perceptible growing mass. The possibility, 



* Male W238 may have possessed a genetic constitution which would have 

 allowed at least temporary growth of the unaltered dBrA tumor — the exceptional 

 dBrA showing successful temporary growth in a number of mice was in him able 

 to continue its growth. 



