126 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



especially the necrotic areas. Fibrous tissue formed in larger quantity around 

 the heterotransplant of cartilage than around that of thyroid or of kidney, 

 probably because cartilage was less rapidly destroyed and its effect on the 

 host tissue extended therefore over a longer period of time ; however, a similar 

 reaction could take place also around heterotransplanted thyroid and kidney 



TABLE III 



in the course of the second week. In accordance with the large amount of 

 fibrous tissue produced especially around heterotransplanted cartilage and fat 

 tissue, large masses of lymphocytes accumulated in the surrounding connective 

 tissue at some distance from the graft; a similar reaction could also occur 

 around other kinds of grafts, but it was observed more rarely in such tissues 

 as thyroid, skin and kidney, as a rule, probably because these were destroyed 

 by the heterotoxins more rapidly than cartilage. 



Exchange of tissues between rat and mouse. In addition to the transplan- 

 tations mentioned above, we carried out also heterotransplantations of tissues 

 from rat to mouse and from mouse to rat, on the assumption that between 

 these relatively nearly related species the reactions against heterogenous grafts 

 might be less severe. However, we found that the reactions did not differ in 

 severity essentially from those obtained in transplantations between the other 

 species which we had tested. Transplantations from rat to mouse and recipro- 

 cal transplantations caused much more severe injury than homoio- and even 

 inter-racial transplantations. Not only was the damage greater if we consid- 

 ered the average results obtained in a number of individuals, but in each in- 

 dividual case it was very great. Moreover, the individual variations which we 

 have found between different homoio- and inter-racial transplants were almost 

 absent in this series and this lack of variation applied to heterotransplantations 

 in other species as well. Only the time of survival of the cartilage hetero- 

 transplanted into mouse or rat showed more marked differences ; in some cases 

 it became necrotic at an early period following the transfer into the hetero- 

 genous host, while in other cases it could survive for almost four weeks, or 

 even somewhat longer. But the degree of this variability was more apparent 

 than real, inasmuch as even under the best conditions the new formation of 

 cartilage by perichondrium, which is found around necrotic or damaged car- 



