GENERAL CONSIDERATIONS 29 



in which there is only a relatively slight divergence in the constitution of the 

 individuality differentials. 



(c) There are also differences in the reactions of different strains, belonging 

 to the same species, against strange individuality differentials. Such differ- 

 ences might be expected in the reactions between individuals from strains 

 which have been inbred to different degrees. The less close the inbreeding, the 

 more severe will be the average reaction between different invididuals. Fur- 

 thermore, a strain whose genetic constitution differs markedly from that of 

 another strain may be expected to react strongly against individual mem- 

 bers of the latter strain. But in addition, there is some evidence that different 

 strains and also different individuals are able to react more strongly against 

 strange strains and individuals than are others. Thus, among rats it seems 

 that Busch strain rats reacted, on the average, more severely against individ- 

 uals belonging to various strains than did strains of a different origin. 

 Furthermore, among mice there is some indication that strain C57 tended to 

 react more readily with lymphocytic infiltration of a strange tissue than did 

 other about equally inbred strains. However, this observation is at present 

 only a preliminary one; it needs further study and confirmation. There are 

 also indications that certain individual animals exhibit a stronger reaction to 

 the tissues of various other individuals than do other animals of the same 

 strain. We must, therefore, in evaluating jthe significance of certain reactions 

 as tests for the constitution of individuality differentials, consider the possi- 

 bility that there exist some variations in the strength of the reactions which 

 are independent of the degree of difference in the constitution of these differ- 

 entials. 



(d) As to the differences in the reactions against different tissues, all 

 derived from the same individual and transplanted into the same host, these 

 are quite marked. Tissues differ in respect to their resistance to injurious con- 

 ditions and therefore in their ability to survive following transplantation. 

 There are quantitative variations in this respect between different types of 

 tissues. Some, as for instance, adult ganglia cells, which are severely injured 

 by a short interruption of oxygen supply during and following the process of 

 transplantation, cannot be successfully transplanted. Under ordinary condi- 

 tions it is more difficult to graft, for any length of time, the adrenal cortex 

 into a homoiogenous individual than the anterior hypophysis. Cartilage and 

 perichondrium are very resistant to injuries associated with the process of 

 transplantation ; they withstand also relatively successfully an attempted in- 

 vasion by lymphocytes and connective tissue, although even in this respect 

 differences exist between very cellular cartilage and cartilage in which the 

 intercellular substance predominates. Dense fibrous hyaline tissue resembles 

 to some extent cartilage. Intermediate in their behavior following transplanta- 

 tion are kidney, fat tissue, salivary glands, and some glands with internal 

 secretion, such as ovary and thyroid ; and among each of these various organs 

 different constituents are graded in their power of resistance, thus the ex- 

 cretory ducts are usually more resistant than the specific functioning paren- 

 chyma. 



