PROCESSES OF IMMUNITY 159 



the active immunity could establish itself. There were, in addition, the experi- 

 ments of Fichera, who showed that it was possible to immunize rats against 

 grafts of rat embryo by successive transplantations of the tissues of rat 

 embryos, and those of Peyton Rous, who obtained similar results with mouse 

 embryos. Likewise, repeated transplantation of adult skin seemed to lead to a 

 more active destruction of the last transplant. There may be cited, besides, 

 the finding of von Dungern, that rabbits could be immunized against the 

 tracheal epithelium of cattle, which was then more rapidly destroyed by the 

 bodyfluids of rabbits. Subsequent investigators, as for instance Lehmann and 

 Tammann, as well as Fischer, assumed that the development of an active im- 

 munity was the cause of the lack of success in homoiotransplantation. The 

 former conceded, however, that with a heterogenous serum a primary toxicity 

 may play a certain role, but that this would be of slight importance in homoiog- 

 enous transplantation. 



In addition to the active immunity, some other factors were thought to cause 

 the destruction of homoiogenous transplants. Ehrlich had observed that 

 growth of a first tumor could prevent the growth of a second tumor in certain 

 cases, and he also noted that transplantation of a tumor piece into a pregnant 

 animal did not succeed well : he interpreted these effects as being due to a com- 

 petition for specific foodstuffs, in which an established tumor or a growing 

 embryo had the advantage over a recently transplanted tumor, which thus, 

 suffered from athrepsia. To this factor, starvation, Ehrlich attributed also 

 the slow death which a mouse tumor underwent when it was transplanted to a 

 rat. In a similar way Schoene explained the fact that homoio- or heterotrans- 

 planted skin could be successfully re-transplanted to the original donor after 

 it had been in the new host for three days, whereas, after a period of four days 

 the injury of the skin graft was so severe that a successful retransplantation 

 was no longer possible. 



Among still other factors considered as responsible for the death of homoio- 

 transplanted tissues, may be mentioned lack of function. The importance of 

 this factor was especially indicated by an experiment of Jores, which showed 

 that electric stimulation exerts a beneficial effect on transplants of striated 

 muscle. Also, deficient nourishment and older age of the host resulted in less 

 successful transplantation, as did also, according to Ribbert, differences in the 

 composition of the inorganic salts of host and donor. Schoene accordingly be- 

 lieved that factors, such as favorable conditions for function and nourishment 

 in the host, may make possible a successful homoiotransplantation. However, 

 less significance was attached to these factors by later investigators, who, as 

 stated previously, stressed above all the importance of an active immunization 

 of the host against the transplant as the cause of the destruction of homoiog- 

 enous and heterogenous grafts. That so little importance was attributed to 

 the primary incompatibility between the bodyfluids and tissues of host and 

 transplant seems to have been due largely to two factors. In the first place, the 

 reactions taking place between the hemolysins and bacteriolysins, the agglu- 

 tinins and precipitins, which were considered as types of primary toxins, 

 and the cells providing the antigens occur very rapidly and inasmuch as so 



