EXCHANGE OF TISSUES BETWEEN VARIETIES 133 



fest, the principal injurious effect being that exerted by the cells of the host. 

 If the bodyfluid was injurious in a given host, it acted on the various organs 

 and tissues from the same donor in a corresponding manner. These various 

 tissues from the same donor must therefore all have possessed the same 

 individuality differential ; otherwise the bodyfluid from the same host could 

 not have acted on all of them in this way. If we consider in a general way the 

 cellular reactions of the host against the transplants and the structural changes 

 in the latter, in these various series, we find that the degree of necrosis in the 

 grafts and the degree of the substitution of the necrotic tissue, by fibrous tissue 

 as well as the extent of the invasion of living tissue by fibrous tissue, became 

 greater with increasing distance in relationship between host and donor. Like- 

 wise, the lymphocytic infiltration was the more marked the greater the distance 

 in relationship between host and graft, provided the difference between the or- 

 ganismal differentials was not so great that it led to extensive necrosis of the 

 graft and largely to the replacement of the necrotic issue by fibrous tissue. 

 Such a graded replacement by connective tissue and also by lymphocytes could 

 be followed especially clearly in the transplanted fat tissue ; but on the whole, 

 the lymphocytic infiltration was more marked around and in the thyroid than 

 in the cartilage-fat tissue transplants, and as a rule there was a correspondence 

 between the reactions against the thyroid and cartilage- fat tissue. In autog- 

 enous transplantation of the thyroid in Gray Norway rats the connective 

 tissue tended to be loose, fibrillar-cellular rather than fibrous-hyaline, the 

 blood and lymph vessels were prominent in the center of the transplant and 

 marked lymphocytic infiltration was lacking. 



While the reactions in transplantations between different races in rats 

 varied in intensity in individual cases, they still fell within that part of the 

 spectrum of reactions which characterizes homoiogenous relationship ; but 

 within the homoiogenous range of the spectrum they were situated at the 

 end farthest removed from autogenous relationship. Notwithstanding the con- 

 siderable degree of individual variations in the intensity of the reactions, the 

 best grades attained in the interracial series did not equal the highest grades 

 reached in typical homoiotransplantations ; but there is no sharp break in 

 these cases between the character of homoiotransplantations and of inter- 

 racial transplantations, such as is found if we pass from homoiogenous or 

 interracial transplantations to transplantations between nearly related mam- 

 malian species. 



In a former smaller series VI in which thyroid, cartilage, fat tissue 

 and bone were transplanted from white rats to cream or hooded rats and the 

 examination took place after the grafts had been kept in the host for 20 and 

 21 days, the transplants of the thyroid gland were all destroyed or only a few 

 acini were found, and these were compressed by connective tissue and in 

 process of destruction by lymphocytes; likewise in the fibrous tissue as well, 

 that had replaced the destroyed thyroid, there was still some lymphocytic in- 

 filtration. In the cartilage transplants the fat tissue was infiltrated or mostly re- 

 placed by fibrous tissue and there were variable amounts of lymphocytic infil- 

 tration. Perichondria! regeneration of cartilage around necrotic cartilage was 



