HETEROTRANSPLANTATION 129 



mammalian or avian tissues into the frog was very injurious, but it is doubt- 

 ful whether this result was entirely due to distance of phylogenetic relation- 

 ship; it is possible that bacterial infection played a role in this instance. 



Evidently the heterotoxic action in general is so strong that all hetero- 

 transplanted tissues are near the threshold of destruction and the factor of 

 phylogenetic relationship becomes thus of minor importance; under these 

 conditions, a little more or a little less intense heterotoxic action may be of 

 less importance than some other factor of a secondary nature. Thus there is 

 some indication that the guinea pig may represent a host more unfavorable 

 to certain heterogenous tissues than the rat or rabbit. 



(2) As to growth processes in the heterotransplants, these were very slight, 

 as might be expected in view of the injurious action of the heterotoxins. The 

 mitotic activity usually ceased from one to a few days before the complete 

 necrosis of the transplant occurred. The continuous destruction of the hetero- 

 transplant is not therefore compensated by a marked new formation of tissue. 

 Heterotoxin prevents the full recovery of the tissues after transplantation 

 and causes their death after a relatively short time. Correspondingly, certain 

 regenerative processes which are found quite normally in cases of homoio-, 

 and even in inter-racial transplantations, are lacking after heterotransplanta- 

 tion ; this includes, for instance, the new formation of cartilage from the peri- 

 chondrium, as well as the multiplication of nuclei in striated muscle tissue. 

 In a few exceptional cases, at early periods, there were possibly some indi- 

 cations of weak regenerative processes, but the interpretation in these in- 

 stances was doubtful. Only in transplantation from Peromyscus to mice of 

 strain C57, restricted regenerative growth was noted within the first two 

 weeks after grafting; in one case, even a mitosis was seen in a young car- 

 tilage cell, but here, also, the growth soon ceased. It seems that for the 

 same reasons, namely, the interference of active heterotoxins, it is difficult 

 for the host capillaries to make connection with the capillaries in the trans- 

 planted tissue and to use these preformed channels for the establishment of 

 blood circulation in the transplant, the grafted vessels presumably dying soon 

 after transplantation; furthermore, this factor may be responsible for en- 

 gorgement of the surrounding vessels and for hemorrhages into and around 

 the transplant. (3) The difference in the fate of different heterogenous tis- 

 sues used, such as thyroid, skin and kidney, was very slight; they all be- 

 haved in almost the same manner after heterotransplantation ; only cartilage 

 was definitely more resistant, as it was also in homoiotransplantation. It fol- 

 lows from these observations that the method of heterotransplantation is not 

 suited for the determination of species differences ; serological tests are pref- 

 erable for this purpose. In this respect, heterotransplantation differs from 

 homoio- and syngenesiotransplantation, in which latter, especially the cellu- 

 lar reactions as a rule are very fine indicators of the degree of relationship 

 between individuality differentials of host and donor and in this respect 

 are superior to serological tests. Transplantation as a method for the deter- 

 mination of individuality differentials may be compared to a delicate balance, 

 able to distinguish between fractions of a milligram but ill-adapted to the 



