24 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



ence of certain conditions in the bodyfluids of the host, which determine the 

 suitability of the animal's own autogenous bodyfluids and the unsuitability of 

 homoiogenous bodyfluids for the transplant. This conception implies a factor 

 in common to the bodyfluids and to the cells of each individual. In subsequent 

 investigations to which we have referred already also Todd (1913) recognized 

 the existence of a factor common to and characteristic of all the cells of an 

 individual ; but according to this investigator in near relatives this factor 

 might be the same. (2) Growth factors inherent in the transplant, and 

 (3) extraneous growth factors circulating in the bodyfluids of the host, similar 

 to those given off by the ovary under certain conditions. These observations 

 were subsequently confirmed by Borrel, Ribbert, and they were extended to 

 malignant tumors by Bashford and Tyzzer. In 1909, Borst and Enderlen re- 

 ferred the difference between auto- and homoiotransplantation of blood vessels 

 to "biochemical differences" between individuals of the same species. How- 

 ever, as we shall show later, these "biochemical differences" are not identical 

 with individuality and species differentials. With Addison, we extended our 

 investigations as to the effect of the phylogenetic relationship of tissues be- 

 longing to different species on the fate of the transplants, and Schoene studied 

 the influence of family relationship on transplantability. In the following 

 years, W. Schultz analyzed the relation between hybridizability and trans- 

 plantability of skin. In the meantime tumor transplantations had been carried 

 out on a large scale, and while at first, especially in the work of Jensen and 

 Ehrlich, problems of immunity played a prominent role in the analysis of con- 

 ditions which determine the result of transplantations, we and, subsequently, 

 Peyton Rous used the transplantation of tumors as a method for studying 

 tissue growth in general and we emphasized the close relations which exist 

 between the growth of normal tissues and of tumors. 



The writer, in association with Addison, Myers, Hesselberg and others, 

 noted the significance of lymphocytes, and also of fibroblasts and vascular 

 endothelia, in the reaction of the host against the transplant. In the case of 

 tumors, it is especially the various investigations of Murphy and his collabora- 

 tors which subsequently showed the significance of lymphocytes in the re- 

 sistance of animals against inoculated pieces of cancers. In normal tissues we 

 found that the time of appearance and the intensity of the lymphocytic reac- 

 tion developing around a transplant in combination with connective-tissue and 

 blood-vessel reactions, could be used in testing quantitatively the genetic re- 

 lationship between host and donor. We formulated thus, in the following 

 years, the concept of organisnial differentials, and we analyzed the genetic 

 relationship between host and transplant and the fate of the latter. Qosely 

 inbred strains of mice were used for the analysis of the factors determining 

 the growth of transplanted tumors, especially by Little and his collaborators, 

 and we extended use of such strains to the analysis of the organismal differen- 

 tials of normal tissues. There developed hence, step by step, mainly as the 

 result of greatly varied transplantations of normal tissues in which simultane- 

 ous multiple and successive transplantations proved of special value, the con- 

 ceptions of various kinds of specificity in tissue and organ relations, of the 

 autogenous equilibrium of the organism and of tissue reactions as a test for 



