68 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



breeders in different cities. Various combinations of donors and hosts were 

 tested, and in a number of experiments tissues from one donor were placed 

 into the left side, and those from another donor into the right side of a host; 

 in other cases, pieces of tissues from the same donor were transplanted into 

 two different hosts. In the majority of these experiments the examinations 

 took place 20 days after transplantation. 



In order to compare the intensity of the reaction in different combinations 

 of hosts and transplants it is necessary to make equal the times at which the 

 examination takes place. With increasing time, the severity of the reactions as 

 a rule increases. If we consider all these experiments together, we may con- 

 clude that autotransplantation, where the individuality differentials of host and 

 transplants are identical, reactions which do occur are due to injury inflicted 

 on the grafted tissue during the operation or to the abnormal conditions under 

 which the transplants live in their new environment, and that these abnormal 

 conditions are, as a rule, overcome in the course of time. On the other hand, in 

 the case of homoiotransplantations the reactions are caused by the differences 

 in the individuality differentials between host and transplants, and in different 

 combinations of families or strains the severity of the reaction in the host and 

 the injury in the donor differ. While in some combinations the reactions are 

 severe, as indicated by grade 1, in others the grades range between 1 and 2— ; 

 in still others the average grade may be 2—, or even somewhat higher, and in 

 rare instances, grade 3 — , or even 3, may be reached in an animal. These grades 

 apply only for a certain length of time, during which the transplant was ex- 

 posed to the influence of the host ; this period was 20 days in this series of 

 experiments and there are indications that after 30 or 40 days the reactions 

 would have been more severe and the grades accordingly lower. Essentially 

 two factors are responsible for the grades thus obtained. In the first place, 

 these differences in the reactions are due to differences in the relationship be- 

 tween the individuality differentials of host and donor. This is indicated by the 

 fact that if various tissues are transplanted from one donor into the same 

 host, the severity of the reaction is the same in all the pieces, if we make 

 allowance for the peculiarities which distinguish different types of tissues. 

 This conclusion harmonizes with the many other transplantations which we 

 have carried out with homoiogenous tissues. Thus, in a certain experiment in 

 which grade 3 had been given, a great portion of the thyroid transplant was 

 preserved ; in the muscle transplant there were long parallel muscle fibers with 

 good cross-striations, and in one specimen of this kind even a mitosis seemed 

 to be present in a muscle cell. Likewise, the grafted fat tissue was well pre- 

 served. With grade 2 there was much lymphocytic infiltration in thyroid and 

 muscle and at least a large part of the fat tissue was preserved, while with 

 grade 1, neither thyroid nor muscle was preserved and the fat tissue was 

 mostly replaced by connective tissue, small vacuolated cells and lymphocytes. 

 Furthermore, it could be seen that the individuality differentials of both host 

 and donor determined the intensity of the reactions; this follows from ex- 

 periments in which either the donor or the host varied, while the other partner 

 which entered into the combination remained constant. The lymphocytic reac- 



