396 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



a strange individuality differential. This increase in growth energy, other 

 factors being equal, must lead to an increase in the number of developing 

 tumors, and indeed, under these conditions there can be observed a paral- 

 lelism between increase in growth energy and number of takes. Secondly, 

 there may take place in the tumor more specific changes of an adaptive 

 character ; the strange individuality differential of the host seems to alter the 

 tumor in such a way that it becomes less sensitive to the injurious action of 

 the strange differential. In diminishing the injurious effects of the host this 

 change itself also may, under certain circumstances, secondarily cause an 

 increase in the growth energy of the transplant. Whether a strange differential 

 will act merely injuriously on a tumor, whether it will also have a stimulating 

 effect, or whether, in the end, it will produce adaptive changes, depends pre- 

 sumably upon quantitative relations between the degree of strangeness of the 

 individuality differentials and the inherited power of resistance and other in- 

 herited characteristics, such as a certain modifiability of the tumor cells. 



It may then be stated that transplantability, as judged by the number of 

 takes of a tumor, is contingent largely on the relation between the organismal 

 differentials in host and transplant, and on the ability of the tumor cells to with- 

 stand injurious influences of not well suited organismal differentials. The 

 latter factor depends, among other conditions, also on the actual or potential 

 growth energy of a tumor and on the ability of the tumor cells to undergo 

 adaptive changes in different environments. The organismal differentials in 

 host and tumor are determined directly by their genetic constitution, but the 

 range of the potentiality of adaptation, the increased growth momentum, 

 and the ability to undergo variations in growth energy are only indirectly de- 

 termined by genetic factors transmitted by the germ cells ; directly, they are 

 determined by environmental factors which are active during the transforma- 

 tion of normal into cancerous tissues. 



This relatively high degree of adaptability to different environmental condi- 

 tions which we observed in tumors, distinguishes them from normal tissues, 

 in which such an adaptive, plastic character of the cells cannot be demon- 

 strated. For instance, attempts to overcome the action of unfavorable individu- 

 ality differentials in the host by serial transplantation of normal tissues did 

 not succeed. Thus, in our serial transplantations of epidermis the transplants 

 soon died and while we found that cartilage cells could be transplanted 

 serially and live for a long time — much longer than the animal in which this 

 tissue originated — in the end they also died and the serial transplantation 

 ended. It is possible that this difference between normal and tumor tissues is 

 due to the difference in the growth energy which exists between these types of 

 tissues. The greater growth energy which cancers possess makes it possible 

 for them to resist difficulties which would destroy normal tissues, and gives 

 the former a chance to react to a new environment with adaptive changes. But 

 there is also the probability that the changes which take place in normal tissues 

 when they are transformed into tumor tissues, introduce at the same time a 

 new type of adaptability to strange organismal differentials, which normal 

 cells do not yet possess ; this power of adaptation would then represent a newly 



