134 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



only rarely seen. If we use the second type of grades, the average grades in 

 these two last named series was 1.75 and 1.5, respectively. In ordinary trans- 

 plantations among white rats, carried out at the same time, the average reaction 

 was 2.8. In this series of interracial transplantations, also, there was a corre- 

 spondence between the degree of genetic relationship between donor and host 

 and the degree of the reactions against the transplants. Regeneration of 

 cartilage by perichondrium was inhibited, but not entirely prevented. The bone 

 marrow became necrotic and was replaced by fibrous tissue at an early date, 

 while in homoio- and syngenesiotransplantations the marrow could remain 

 preserved for a longer time; in agreement with the findings in other experi- 

 ments, cartilage remained as a .rule preserved, at least in part. 



In series VII in the mouse, we carried out transplantations of thyroid, 

 cartilage and fat tissue from wild gray mice to mice belonging to the inbred 

 A and Old Buffalo strains. In general, the results corresponded to homoio- 

 genous reactions, which were more severe in the series in which Old Buffalo 

 mice were the hosts. In this series the thyroid transplant had been destroyed 

 in animals examined later than 12 days. In the fat tisssue there was more and 

 more ingrowth of connective tissue, as well as of vacuolated phagocytes, and 

 after 16 and 25 days there was much infiltration with lymphocytes. In the 

 mice from the A strain the thyroid was present up to 20 days, but it was 

 stunted or incomplete and the organization of the necrotic center proceeded 

 only slowly. Here, also, more and more connective tissue and vacuolated cells 

 grew into the fat tissue, and, in some cases, the lymphocytic infiltration was 

 quite marked. The transplanted bone marrow became replaced by connective 

 tissue in all instances. However, in several animals some muscle fibers with 

 nuclear chains were found in both strains of mice. There is, then, no sharp 

 demarcation between these experiments and others in which homoiogenous 

 tissues elicited severe reactions; the grades varied between 2— and 1, and the 

 latter grade was obtained in the mice examined at the later dates. On the 

 whole, there was a remarkable correspondence in the reactions against differ- 

 ent tissues from the same donor in the same host. This applies to all of these 

 transplantations and it comes out clearly, for instance, in series III, the 

 intraracial transplantations. Polymorphonuclear leucocytes were not found, 

 as a rule, in these experiments ; if seen at all, they appeared especially in the 

 fat tissue. 



The main result which emerges from these investigations is, then, the dem- 

 onstration that the reactions against tissues from different races or subspecies 

 correspond to very severe homoiogenous reactions, and that they differ from 

 heterogenous reactions in several respects. Furthermore, inasmuch as the race, 

 Curly Coat, differs from Gray Norway in one single mutation, it may be con- 

 cluded that such a mutation may have a definite effect on the individuality 

 differential. 



If we compare these transplantations between individuals belonging to 

 different races with those in which donor and host belong to different species, 

 the grades applied do not completely correspond to each other. This is par- 

 ticularly true of grade 1, the severest grade. In both of these types of trans- 



