230 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



entials incompatible with those of the host. In principle, conditions are 

 therefore similar to those found by us in the case of mammalian tissues; a 

 difference exists only in that the reactions in urodeles were slower than in 

 rodents, and also in that lymphocytes and fibroblasts later destroyed parts 

 of the autotransplants, while other parts remained preserved ; these reactions 

 against autogenous tissues were presumably due to necrobiotic changes which 

 occurred in certain areas of the grafts. In both urodeles and mammals the 

 vascularization of autotransplants was better than that of homoio- and hetero- 

 transplants. 



Also, Hitchcock finds that frog skin autotransplanted into the lymph sac 

 of frogs remains preserved much longer than heterotransplanted skin. Ulti- 

 mately, however, it is destroyed through the ingrowth of fibroblasts ; but this 

 result is due merely to accidental factors and not to factors inherent in 

 amphibian tissues, as is evidenced by the fact that skin autotransplanted into 

 a defect of skin remains preserved indefinitely. Similar results may be obtained 

 in mammals and birds, for example, when skin is injured after autotrans- 

 plantation into the subcutaneous tissue. Following heterotransplantation of 

 frog skin, the transplant is destroyed much more rapidly than after autotrans- 

 plantation and the destruction takes place the more rapidly the farther distant 

 phylogenetically the species of host and transplant; frog skin dies very 

 quickly after transplantation into Triturus and Triturus skin becomes necrotic 

 within a very short time after transplantation into the frog. After trans- 

 plantation into urodele species, it is the heterotoxin of the bodyfluids which 

 kills the transplants, while after heterotransplantation into Rana, the injury 

 is due, above all, to the action of leucocytes. In the tissue surrounding the 

 graft, lymphocytes accumulate. Conditions here are therefore, in principle, 

 similar to those after heterotransplantation of mammalian and avian tissues; 

 only in the latter the injurious action of the bodyfluids is evident in every 

 instance, while, according to Hitchcock, this effect is not noticeable after 

 transplantation of frog skin into more nearly related species. Presumably we 

 have, in the case of frog skin, to deal merely with quantitative differences 

 in the effects of toxins and of cellular reactions, such as were observed also 

 in the case of mammalian tissue, where we noted that heterotransplantation 

 of cartilage produced cellular reactions which were much more prominent than 

 those following heterotransplantation of such very sensitive tissues as thyroid 

 and kidney, which are destroyed by strange bodyfluids within a very short 

 time. We have found also other instances of quantitative differences between 

 the respective importance of toxic serum and cellular reactions in different 

 species of mammals. It has been assumed in the case of tumor transplantation 

 that necrosis primarily attacks the center of the pieces and not the peripheral 

 parts, which indicates that an injurious action of the bodyfluids on the trans- 

 plant is lacking. Hitchcock uses the same argument in order to prove the 

 absence of an injurious action of the bodyfluids after transplantation of skin 

 of Rana into strange species of Rana. Nevertheless, homoiotoxic action does 

 exist in the case of tumors as well as of normal mammalian tissues; and we 

 may draw the same conclusion in regard to heterotoxic action in heterotrans- 



