BLOOD VESSEL ANASTOMOSIS 175 



strated in parabiosis, although it seems that under special conditions hemol- 

 ysins may develop. Thus Irwin found that in two different races of doves, 

 in which no blood groups can be shown to exist, hemolysins may be pro- 

 duced ; but in this case we have to deal not with a homoiogenous parabiosis, 

 but with one approaching a heterogenous type. Also, Majeda states that he 

 has observed the presence of hemolysins in a few cases. But the other 

 investigators who have searched for hemolysins in parabiosis did not find 

 them ; or in those instances in which they were present, they had, in all 

 probability, not been produced in response to the action of blood group 

 antigens in the other partner, the existence of which could not be established, 

 but they may have been due to the antigenic action of certain heterogenous 

 or homoiogenous gene sets or their derivatives. The usual absence of the 

 ordinary immune substances in parabiosis renders improbable also the exist- 

 ence of antibodies responsible for a state of anaphylaxis. 



We suggested (1930) the possibility that substances which carry the 

 individuality differentials are given off in small quantities by various organs 

 of one partner and enter the circulation of the other, and that these may 

 account for the gradually developing disharmony, the increasing atrophy of 

 organs, and the weakness in the partner which was inferior from the be- 

 ginning. Such substances may be expected to stimulate the lymphocytic and 

 also the reticulo-endothelial system of tKe other partner, in accordance with 

 the usual stimulation of lymphocytes in ordinary homoiogenous transplanta- 

 tion. These homoiogenous substances may thus conceivably function as very 

 slowly acting toxins and secondarily may give origin also, although only 

 feebly, to immune substances specifically directed against the individuality 

 differentials of the partner. 



In favor of this view, several facts may be cited : in the first place there 

 is a parallelism between the genetic relationship of the parabionts and the 

 rapidity with which disharmony is established and the intensity of the latter. 

 As we have mentioned, the success of parabiosis essentially parallels the 

 relationship of host and donor, in the same sense in which success of trans- 

 plantation depends upon this factor; as in syngenesiotransplantation, es- 

 pecially in inbred strains, where the reaction against the transplant may 

 become manifest only after a long period of latency, so also under favorable 

 conditions of parabiosis the stage of disharmony may develop only after a 

 long preceding harmonious state. Furthermore, the healing of the skin flap 

 at the site of union of the parabionts behaves in a way which approximately 

 corresponds to the genetic or pedigree relationship of the two partners ; the 

 healing-in succeeds the better the more compatible the two partners are 

 with each other and the longer the harmonious phase lasts (Gohrbandt). 

 During the disharmonious state it is especially the stronger partner which 

 reacts more markedly against the skin flap. Of special interest in this respect 

 are also the experiments of Majeda, who transplanted skin from one rat 

 to another preceding and following the establishment of parabiosis. He found 

 that those animals between which skin could readily be exchanged and re- 

 main preserved for some time were better adapted for parabiosis experi- 

 ments, than were other animals in which skin transplants did not heal in a 



