HETEROTRANSPLANTATION 123 



that the differences in the local reaction and the reaction in the circulating 

 blood is due to a greater sensitiveness of the latter, which allows the recogni- 

 tion of homoiogenous differentials in material in which these differential sub- 

 stances are present in so small a quantity that they can not be discovered by 

 the local reaction. But in this instance we have again to consider the possibility 

 that less specific reactions against non-living protein material may participate 

 in these general reactions and that this factor may introduce a complication 

 which is absent in the local reaction. 



There are some additional questions concerning heterogenous transplanta- 

 tions which are of more general interest and which we shall now consider : 

 (1) Does a relationship exist between the time of survival and the growth 

 processes in heterotransplants and the reactions of the host tissue against the 

 latter, on the one hand, and the phylogenetic relationship between host and 

 transplant on the other? (2) What are the relations between growth processes 

 in heterotransplants and time of survival? To what extent do regenerative 

 growth processes take place in heterotransplants? (3) What differences occur 

 in heterotransplantation of different organs and tissues? (4) Do the results of 

 reciprocal heterogenetic transplantations differ and what is the reason for 

 this difference? In order to answer these questions we may discuss briefly the 

 principal results obtained in some of our series of heterotransplantations, 

 while we omit a description of others. * 



Heterotransplantation of guinea pig skin. In association with W. H. F. 

 Addison, we observed that after transplantation of guinea pig skin into other 

 species the epithelial cells grew less actively than after homoiotransplantation, 

 but the growth continued for some time, as indicated by the presence of 

 mitoses in the epidermal cells. Mitoses were found in the rabbit as late as 8 

 days, in the dog, 7 days, and in the pigeon 5 days following transplantation. 

 However, the mitoses were less numerous than after homoiotransplantation 

 and the difference between the activity in the homoio- and heterotransplanted 

 tissue increased with increasing time after transplantation. In heterotrans- 

 plants the mitotic activity usually ceased a few days before the tissue became 

 entirely necrotic ; but, it happened that a mitosis could be seen near the time 

 of death. The hair follicles, which are burrowed deep in the tissue and are 

 surrounded by a connective tissue capsule, thus being most effectively pro- 

 tected, remained alive longest and showed the greatest number of mitoses. 

 Also, the cells of the surface epidermis lived for some time and continued to 

 produce keratin; the connective tissue of the host surrounded the trans- 

 planted epidermis ; yet the growth energy of the epithelium was too weak to 

 cause a cystic distention of the transplant from pressure of the newly pro- 

 duced keratin, in contrast to the finding after homoiotransplantation, where the 

 epidermis does, as a rule, form a cyst. However, even the homoiotransplanted 

 tissue may lose this ability if its growth energy has been weakened, as for in- 

 stance, by previous serial transplantation. Lymphocytes migrated into the 

 heterotransplanted epidermis from the surrounding host tissue and they, to- 

 gether with the pressure exerted by the fibrous capsule, helped to destroy the 

 epithelium which had already been injured by the action of the heterotoxins. 



