364 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



suitability of the hosts for the tumor he used ; however, in his experiments he 

 had to deal with mice which belonged to different subspecies. Cuenot and 

 Mercier separated, through breeding of white mice from their locality, fam- 

 ilies in each of which the degree of transplantability was a fixed quantity 

 which was inheritable ; they believed that, through breeding, they had been 

 able to sort out what corresponded to Johannsen's pure lines. But such in- 

 vestigators as O. Hertwig and Poll, and C. Lewin, denied the existence of 

 these differences of susceptibility to tumor transplantation between different 

 families or strains within the same species, and it was especially an experi- 

 ment of Haaland which was responsible for the assumption, subsequently 

 made, that adaptive variations in the animals, taking place in response to 

 changes in the environment, rather than fixed constitutional characteristics 

 were the cause of these differences between different strains. Haaland ob- 

 served that mice bred in or near Frankfurt, which were suitable as hosts for 

 Ehrlich's mouse sarcoma, became unsuitable after they had been transferred 

 to Norway and bred there for a short time. He attributed this change to the 

 difference in the kind of food given to the mice in these two localities and 

 concluded, therefore, that the suitability of hosts for a certain tumor de- 

 pended on variable environmental, rather than on fixed inheritable conditions. 

 Other investigators confirmed Haaland's observations and accepted his con- 

 clusions as to the effect of various kinds of food on the number of takes of 

 a certain tumor. 



On the other hand, our investigations, made in conjunction with M. S. 

 Fleisher (1912), showed that the differences in transplantability occurring in 

 different strains of mice depend upon fixed hereditary conditions, which are in- 

 dependent of environmental factors. American and different types of European 

 white mice, all fed in the same way and bred separately under identical en- 

 vironmental conditions, each maintained its characteristic transplantability in- 

 dex for a carcinoma which had developed spontaneously in an American 

 mouse. Subsequently Morpurgo, and also Roffo, made similar observations. 

 The change which Haaland found in his mice after transfer to Norway was 

 interpreted by us in a different manner, because we noted that in one of our 

 European strains a change in its suitability as host took place as a result of a 

 disease which eliminated a number of families. Evidently a selection had 

 occurred, causing the survival of a family which differed genetically from 

 the rest, and which now began to predominate over the other mice. As a 

 result of this selection process, the transplantability rose considerably in this 

 strain. However, the results of transplantation depend not only on the host, 

 but also on the kind of tumors which are used for inoculation. Thus Haaland 

 noted that if each mouse is inoculated with two different types of tumor, the 

 receptivity of different strains of mice differed for each tumor. As we may 

 now express it, the transplantability depends upon the relation of the in- 

 dividuality or organismal differentials of the host to those of the transplant. 

 But we must make the reservation that, within a certain range, adaptive 

 changes may take place in the tumor cells and that thereby the results may be 

 modified. 



