394 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



rat-adapted mouse carcinoma could not be transplanted in rats previously 

 treated with normal or cancerous mouse tissues, while a previous treatment 

 of rats with rat tissue did not prevent transplantation. We may therefore as- 

 sume that the rat-adapted strain of the Putnoky mouse tumor bears essentially 

 the species differentials of the mouse and it is possible that its apparently in- 

 creased effectiveness in the production of immunity in rats may be due to its 

 growth momentum, which is greater in the rat-adapted strain than in the 

 mouse-adapted strain. Yet, even if the increase in immunizing power which 

 distinguishes the rat-adapted strain from the mouse-adapted strain should 

 not be due to the increased growth momentum, it still would not be necessary 

 to attribute such changes to somatic gene mutations ; instead, it might be at- 

 tributed with greater justification to metabolic changes taking place in the 

 tumor cells, independently of constitutional modifications of the organismal 

 differentials. The same considerations apply to the alterations in the specific 

 immunizing action which, according to MacDowell and his associates, leukemic 

 cells undergo in the course of serial inoculation ; properties are acquired 

 which make these propagated lines of leukemic cells different in various as- 

 pects from the original leukemic cells from which they were derived; and 

 similar observations have been made by Dmochowsky in the case of ordinary 

 cancerous tissues. 



Somewhat related to the experiments with the Putnoky tumor are those of 

 Lumsden, which also indicate that a certain adaptation may take place between 

 a tumor and a heterogenous host of a nearly related species, as indicated by the 

 reaction of the tumor cells in tissue cultures. Lumsden finds that if a mouse 

 carcinoma has been developing in a rat for a week, pieces of this tumor grow- 

 ing in vitro are not injured by the serum of the rat which was the host of the 

 tumor, and in which, therefore, immune bodies have developed against the 

 mouse carcinoma cells ; but such a serum rapidly kills mouse carcinoma cells 

 which have previously been growing in a mouse. Likewise, serum of a rat in 

 which a rat sarcoma has grown is not injurious to mouse tumor cells which 

 have been growing previously in a rat, but it is injurious to mouse carcinoma 

 cells which have been growing in a mouse. Yet such tumor cells, which have 

 become resistant to the effects of heterogenous immune serum acting in vitro, 

 retain their specific sensitiveness to transplantation into a heterogenous or- 

 ganism. A mouse tumor is injured after transplantation into a rat, even if it 

 has been growing previously in a rat. Lumsden assumes, therefore, that the 

 immunity thus acquired by the tumor cells is active only against constituents of 

 the blood and, moreover, that the tumor cells growing in a heterogenous host 

 acquire the ability to use the amino-acids specific for the latter as building 

 stones for proteins, which are no longer characteristic of their own but of the 

 foreign species ; this would imply that the species differential of the tumor 

 cells changes into that of the foreign species. However, all the data known so 

 far point to the conclusion that the animal organism transforms amino-acids 

 into protein of its own kind. The adaptation occurring in the tumors growing 

 in heterogenous hosts must therefore be due to processes of a different nature. 



There have thus been established certain variable factors which affect the 



