438 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



used by Tyzzer, Little and Strong. Also, Uhlenhuth, who recognized the 

 species-specific characteristics of tumors, has not apparently considered the 

 relations between the individuality differentials of the tumor and the tissues 

 of the host. He explained the low degree of immunity against spontaneous 

 tumors by the assumption that the defense mechanism against parenterally 

 introduced cells may not be of a high degree of efficiency. Therefore, pieces of 

 spontaneous tumors, even if they possess only a low virulence, can be re- 

 inoculated into the animal in which they originate. Likewise, Caspari assumed 

 that the factors, in particular necro-hormones, which induce immunity against 

 homoiogenous tumors, would be equally effective in the case of autogenous 

 spontaneous tumors. Chambers and Scott ( 1924) regarded immunity against 

 cancer as analogous to immunity against bacteria. They believed a substance 

 is given off during the early stages of autolysis of tumor cells, which acts as 

 antigen and elicits immunity against the cancerous tssue. The reason why 

 spontaneous tumors, and especially human spontaneous tumors, do not call 

 forth immunity in the bearer, in contrast to transplanted tumors, is that in 

 spontaneous tumors the cells are healthy, the implication being that for this 

 reason they do not give off the immunizing substances ; yet, there can be no 

 doubt that autolysing and necrotic areas are frequently found also in spon- 

 taneous tumors. Similar views were expressed also by Woglom (1919). The 

 ready growth of spontaneous tumors in the animals in which they originate 

 is due to an adaptation which has taken place between the tumor cells and 

 the bodyfluids; but there is a general resistance against the growth of spon- 

 taneous tumors as well as against transplanted tumors (1923), and further- 

 more, it needs to be explained why resistance cannot be established in all 

 transplanted tumors (1922). C. Lewin assumed that during the development 

 of a spontaneous tumor, which means, during the transformation of normal 

 tissue cells into tumor cells, the former lose the characteristics which make 

 them constituent parts of the host organism; they behave like foreign cells. 

 He therefore concluded that it should be possible to elicit an immunity reac- 

 tion against a spontaneous, as well as against a transplanted tumor. A cure 

 of a spontaneous tumor would depend therefore on conditions similar to those 

 which determine the retrogression of a transplanted tumor. 



This analysis shows the difference between the views which have been ex- 

 pressed by some of the most prominent investigators concerning the distin- 

 guishing features of tumor growth, the relations between the factors which 

 determine the growth of transplanted tumors and the origin and further 

 growth of spontaneous tumors ; it also presents the interpretations which 

 have gradually developed in conformity with the theory of the organismal 

 differentials. These views are based on some of the earlier observations on 

 tumor growth, which we have discussed already, and on a comparison of the 

 fate of transplanted normal and tumor tissues. All these experiments, as well 

 as those of Tyzzer and Little, and especially the extensive investigations of 

 Little and Strong and their associates on the transplantation of tumors in 

 closely inbred strains, showed the importance of genetic factors in tumor 

 transplantations. Nevertheless, certain differences have developed between 



