402 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



peculiarities secondarily acquired. Also, in the case of transplanted tumors 

 an active immunity develops only if there exists a primary incompatibility 

 of the organismal differentials of host and transplant, although such a primary 

 incompatibility between the organismal differentials of host and transplant 

 may in certain cases be insufficient to prevent the growth of implanted tumors. 

 But, as we have stated already, with tumors an active immunity seems to be 

 of much greater importance in preventing the growth of the transplant than 

 with normal tissues. 



In the majority of cases it seems to be the strange organismal differentials, 

 and in particular the strange individuality differentials, which serve as antigens 

 in the production of an active immunity. Therefore, under normal conditions 

 no immunity develops in mammals against autogenous spontaneous tumors; 

 they are not antigenic. Conversely, because autogenous tumor tissue does not 

 elicit immunity against itself in the bearer of the tumor, it may be assumed 

 that the tumor tissue has essentially the same individuality differential as the 

 other cells of the same organism. However, it has been shown that avian 

 sarcomata and related tumors, produced by means of injections of tumor 

 filtrates, may give origin to antibodies which are active against the autogenous 

 tumor cells ; but these antibodies are directed against the agent and not against 

 the tumor cells. Furthermore, there has accumulated more recently some 

 evidence which proves that in mammalian tumor tissue there may be present 

 in addition to the organismal differentials, some antigens which are specific 

 for a certain kind of tumor and not for the corresponding normal tissue, and 

 perhaps others which are common to many different types of cancer. In these 

 cases, special substances may serve as antigens. 



There has been a certain reluctance on the part of some investigators, 

 especially Bashford and his associates, to apply the term "immunity" to the 

 mechanisms underlying the reactions against tumors developing in animals 

 inoculated with the latter. They preferred the term "resistance," because in 

 the course of time they began to doubt that a typical immunity, comparable 

 to antibacterial immunity, develops at all against cancer cells. This doubt was 

 based on the impossibility of demonstrating immune substances in the host 

 inoculated with homoiogenous tumors and of transferring antibodies to other 

 animals, which thus would be protected against the growth of a second 

 homoiogenous tumor. However, this difficulty has disappeared in recent years, 

 since it has become possible in various ways to demonstrate that such protec- 

 tive substances are formed. We therefore need not hesitate to consider these 

 reactions against tumor grafts as evidence of an active immunity. The 

 processes of active immunity are of special importance as far as the reactions 

 against homoiogenous tumors are concerned. In heterogenous tumors the 

 primary incompatibilities between host and graft become so strong, particu- 

 larly with increasing distance between the species of the host and the bearer, 

 that preformed processes may be sufficient to injure and kill the transplants. 



An active immunity against inoculated tumors may be obtained under the 

 following conditions : ( 1 ) When a transplanted tumor grows in an animal ; 

 the developing immunity is known as "concomitant immunity"; (2) in cer- 

 tain cases following the extirpation of a growing homoiogenous tumor; here 



