TRANSPLANTATION OF PIECES OF TISSUE 253 



Transplantation of embryonal material into the allantoic of chick embryos. 



The first transplantations on the chorio-allantoic membrane of the chick were 

 made with thin pieces of mammalian tumors, and these experiments indicated 

 the great tolerance for heterogenous tissues which this organ exhibits. How- 

 ever, the chorio-allantoic membrane was used also for transplantation of 

 embryonal material and a survival of the grafts was here observed when 

 transplantation into the adult chicken would have been followed by the rapid 

 destruction of the grafts. Thus Hoadley, Murray and others, found that 

 sense organs and extremities of very young, one or a few days old chick 

 embryos develop well, although apparently not always quite normally or 

 completely, on the chorio-allantoic membrane of eight- to nine-day-old chick 

 embryos. However, the time during which the transplants continue to grow 

 under these conditions is not longer than about nine days ; even heterotrans- 

 planted tisue can develop during this short period. Hiraiwa and Willier 

 observed that parts of eleven-day-old rat embryos grew well for nine days 

 on the chorioallantoic membrane of the chick; epidermis, hair follicles, car- 

 tilage and bone, were used and grew as well here as in rat embryos of the 

 same age, but the entodermal and nerve structures did not continue to grow 

 and differentiate in this strange host, or at least they developed less well. The 

 age of the embryonal graft seems to influence the fate of the transplant to 

 some extent. Sandstrom noted that kidney tissue from nine-day-old duck 

 embryos healed in on the chick chorio-allantoic membrane without any part 

 of it becoming necrotic. Older embryonal kidney tissue underwent partial 

 necrosis and the necrotic areas persisted the longer in the host the older the 

 embryo was from which the graft was taken; moreover, the activity of host 

 lymphocytes also increased with increasing age of the grafted embryonal 

 tissue. 



The relatively favorable results of heterotransplantations on the chorio- 

 allantoic membrane of the chick are probably due to the fact that the defense 

 mechanisms, the sensitiveness to strange differentials of the host, and the 

 organismal differentials, factors acting in combination or singly, are not yet 

 fully developed in the placental structures of the early embryo. 



Inoculation of mammalian embryonal material into adult mammals of the 

 same species. Here a growth may take place, which at first may be quite rapid, 

 but which then slows up, comes to a standstill, and finally is followed by 

 retrogressive processes. In different species the tendency to active growth 

 and persistence apparently varies. It seems to be very great in the rat, where 

 the transplant may persist for months and even a year, although in most 

 cases the proliferation may continue only from one to four months, when a 

 cessation occurs followed by retrogression. The period of growth is relatively 

 brief in the mouse, retrogression beginning usually after one week (Rous). 

 In the rabbit, after transplantation into the uterus, it appears that only 

 cartilage survives as long as twenty days (Hammond). However, in all of 

 these experiments with homoiogenous tissues there is a great diversity in the 

 results in different experiments, and even in the rat it is only in exceptional 

 animals that the grafted tissues remain active for very long periods. It is 



