124 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



After re-transplantation of the guinea pig epidermis from the foreign 

 species back to the guinea pig, the epithelial cells grew only very weakly and, 

 on the whole, the farther removed the first host species was from the guinea 

 pig, the shorter was the interval after re-transplantation during which mitoses 

 appeared. No growth took place in the guinea pig skin after transplantation 

 into the frog, which is so unfavorable a soil that a piece remaining longer than 

 3^2 hours in this distant species, did not grow after subsequent re-transplanta- 

 tion into the original donor. Guinea pig skin which had been kept in the rabbit 

 for 2 days was able to grow after re-transplantation into its own species, but 

 pieces that had been longer in the rabbit died after re-transplantation; in the 

 pigeon, pieces that remained less than 5 days could be successfully re-trans- 

 planted into the guinea pig, but not if they were left in the former species for 

 a longer time. If we consider merely the duration of mitotic activity and sur- 

 vival after a single heterotransplantation, the order of compatibility for guinea 

 pig skin was approximately as follows: (1) rabbit, (2) dog, (3) pigeon, 

 (4) frog. But in general the differences between these species in these respects 

 were not great, with the exception perhaps of the frog, which had a very 

 injurious effect on the transplanted guinea pig skin. However, this order does 

 not obtain in regard to readiness of re-transplantation of this tissue, because 

 a primary transplantation from guinea pig to pigeon was less injurious to the 

 graft than a primary transplantation to rabbit. 



Heterotransplantation of pigeon skin. In principle, the results were similar 

 after homoio- and heterotransplantation of pigeon skin to those found in the 

 case of guinea pig skin, but there were also some interesting differences. Even 

 after homoiotransplantation of pigeon epidermis the epithelial proliferation 

 was found to be very slight, although epidermis and connective tissue re- 

 mained largely preserved. While the homoiotransplanted guinea pig skin 

 formed a cyst because of its continued proliferative activity and keratin 

 formation, and while, for the same reason, a necrotic area in the guinea pig 

 skin was rapidly replaced by new tissue, the pigeon skin did not give rise to 

 the formation of such a cyst and reparation of necrotic tissue did not take 

 place on account of the lesser growth energy in the transplanted pigeon epi- 

 dermis. 



Heterotransplantation of thyroid gland. Cora Hesselberg and the writer 

 studied transplantation of the thyroid gland in various species, (a) Thyroid of 

 guinea pig to rat: The heterotransplanted thyroid succumbed readily to the 

 action of heterotoxins, remaining preserved for a short time only under the 

 best of conditions. The primary injury of the graft by the bodyfluids of the 

 host was quite noticeable as early as 3 to 5 days after transplantation. The 

 number of mitoses was much diminished, but they still could be seen as late 

 as 9 days after operation ; this was also the latest time at which living tissue 

 could be found. The epithelium was best preserved in the neighborhood of 

 growing fibroblastic tissue and, conversely, growing epithelium seemed to 

 attract the fibroblasts. The latter penetrated also between acini and had a 

 tendency to form dense fibrous tissue, which compressed the acini and con- 

 tributed to their destruction. The vascularization of the graft was very poor, 



