96 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



differentials in brothers and sisters, as compared to non-litter mates, was 

 very definite, in contrast to experiments in non-inbred animals, where these 

 differences between syngenesio- and homoiotransplantations are not always 

 definite. The correspondence between these two variables, pedigrees and 

 individuality differentials is, on the whole, very close, and this is one reason 

 why we thought it worth while to give some of the results obtained in these 

 transplantations with greater detail. Of further interest is the great difference 

 between the results of hybrid-to-parent and the reciprocal transplantations. 

 The former are not, however, identical with homoiogenous transplantations, 

 nor the latter with autogenous ones; but in both intermediate results were 

 obtained, suggesting that the presence in the hybrid of a gene set similar 

 to that in the host may have, beneficial effects, while the presence of unlike 

 factors in the host may intensify unfavorable reactions against the transplant. 



It is conceivable that the presence in the host of a set of genes not present 

 in the donor might lead to differences between the metabolism of host and 

 transplant and that this might, to some degree, influence the aggressive 

 action of the host against the transplant. However, the intensity of the 

 reaction in these transplantations depends essentially upon the presence in 

 the donor of genetic factors not present in the host. In tumor transplantations, 

 Little and Tyzzer (1916) found that in transplantations from hybrids to 

 parent strain, no successful transplantations were obtained, while the 

 reciprocal transplantations gave 100 per cent takes ; they concluded that only 

 one dose of genes is required for successful transplantations. Subsequently 

 (1921/22), Little and Johnson noted that if pieces of spleen were trans- 

 planted from inbred Japanese mice to hybrids between the Japanese and 

 white mice, the results corresponded to those of autotransplantation, while 

 in reciprocal transplantations from hybrids to waltzing mice, the transplants 

 were destroyed in a short time, indicating a strong homoio-reaction. Similar 

 results were published more recently by Little and Bittner. But in these 

 experiments, conditions were selected which made the recognition of inter- 

 mediate results very difficult. This caused a lack of the finer means of measur- 

 ing existing differences between the individuality differentials of donor and 

 host, and led to the assumption of a genetic identity in one type of transplanta- 

 tion, and of a complete lack of similarity of the individuality differentials 

 of host and donor in the reciprocal type, whereas, in all probability, various 

 kinds of intermediate states existed. 



And, lastly, there are at least indications that there exist constitutional 

 inherited differences between some of the inbred families, which determine 

 not only differences in the intensity of their reactions against strange indi- 

 viduality differentials in the transplant, but which also may perhaps influence 

 the degree of toxic action which the transplant exerts on various hosts. While 

 differences in the interaction between hosts and transplants in different 

 experiments may be partly explainable on the basis of differences in the 

 number of generations which have passed since the ancestries of two indi- 

 viduals, belonging to the same family, branched off from each other, it is 

 not probable that this is the only factor determining the differences observed 



