Chapter 6 



Syngenesiotransplantation, Transplantation in 



Closely Inbred Strains, and the Individuality 



Differentials of Near Relatives 



The average genetic relationship between near relatives, such as broth- 

 ers and sisters, parents and children, should be somewhere intermedi- 

 ate between the homoiogenous and autogenous relationship, and, ac- 

 cordingly, the average results of syngenesiotransplantation should likewise be 

 somewhere intermediate between those of autogenous and homoiogenous 

 transplantation. That this is the case is indicated by some experiments to 

 which we have already referred. However, there may be instances in which 

 such intermediate results are not evident, but in which the reactions obtained 

 in syngenesiotransplantation cannot be distinguished sharply from those ob- 

 tained in homoiogenous transplantation. Several conditions might account for 

 this occurrence: (1) It might be due to the fact that even in syngenesio- 

 relationship there may be such a degree of genetic difference between donor 

 and host of the transplant that the threshold determining a reaction charac- 

 teristic of a homoiogenous transplantation has been reached, although the in- 

 dividuality differentials of donor and host actually are more nearly related 

 than is the case in the average of homoiogenous individuals. (2) It might 

 also be due to the fact that when the threshold determining the homoiogenous 

 reaction is very close to the autogenous region in the spectrum of reactions, 

 the host cells are extremely active and efficient in discovering differences in 

 genetic relationship and therefore the transplants, whose individuality differ- 

 entials deviated only slightly from those of the host, are attacked with a 

 maximum intensity, a type of reaction which we have found to obtain in 

 birds. In those instances in which the individuality differentials of host and 

 donor in ordinary syngenesiotransplantation are so far removed from each 

 other that a mitigated reaction can not be demonstrated, an experimental in- 

 tensification of the brother-sister relationship, through inbreeding, may make 

 the genetic relationship closer than it is in ordinary brother-sister relationship. 

 In this event the threshold point separating homoiogenous and syngenesious 

 reactions may not yet have been passed and the difference in the reaction of 

 the host against the tissues from a brother and from a not so nearly related 

 individual belonging to the same inbred family or strain may then become 

 manifest. In all essential respects, transplantations in closely inbred strains 

 represent intensified brother-and-sister relationships, because the closely 

 inbred strains were obtained by brother-sister matings in consecutive gen- 

 erations. Theoretically, it would be expected that after a certain number 

 of consecutive brother-sister matings have been made, the relationships even 

 between individuals in the inbred strain other than brothers and sisters, 



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