TRANSPLANTATION OF PIECES OF TISSUE 255 



ing factors in these experiments. Similar effects may be observed also after 

 homoiotransplantation of several pieces of adult mammalian tissue into the 

 same host, as we have pointed out in a previous chapter. 



In a relatively small number of experiments, various investigators trans- 

 planted embryonal material into the mother from which the embryo had been 

 obtained ; in some of these cases pregnancy continued, while in others it was 

 interrupted. Freund found no difference in the rat between syngenesio- 

 transplantation, that is, grafting of the embryo to its own mother, designated 

 by this author as autoplastic transplantation, and homoiotransplantation, 

 grafting of embryonal tissue to a strange host; but, considering the wide 

 range of variations which has normally been found after homoiotransplanta- 

 tion of embryonal material, the number of experiments of this kind was not 

 sufficiently large for definite conclusions. In contradistinction to Freund, 

 Fichera noted that in rats the embryonal transplants persisted longer and 

 more tissues developed in the own mother than in homoiogenous hosts. A 

 similar result was obtained by Rous in the mouse. While the growth of the 

 embryonal material was not more rapid in the mother than in favorable 

 homoiogenous animals, in the former it persisted longer and led to the 

 development of a greater variety of tissues. Thus it seems that even in the 

 case of embryonal material the individuality differential, or its precursor, 

 plays a certain role. Nicholas attempted to transplant embryonal limb or eye 

 from brother to brother in the uterus, but technical difficulties made a suc- 

 cessful transplantation only exceptional, and the effect of a close relationship 

 between host and transplant in these experiments remained, therefore, un- 

 certain. Likewise, reports as to the part played by pregnancy in the host on 

 the fate of transplanted embryonal material are contradictory. Freund be- 

 lieved that such tissue grows better in pregnant than in non-pregnant hosts. 

 However, according to Peyton Rous, in the mouse pregnancy inhibits the 

 growth of transplanted embryonal material in a similar manner to that of 

 tumor transplants. 



Through repeated implantation of the embryonal tissue a relative immunity 

 against the growth of subsequently inoculated embryonal tissue can readily 

 be demonstrated, while in adult tissue such an immunity cannot be recognized 

 with the same degree of definiteness. Both Peyton Rous and F. Fichera noted 

 the development of this type of immunity; Rous produced a relative im- 

 munity in the mouse by means of a single inoculation of homoiogenous 

 embryonal material, while Fichera made a series of injections of embryonal 

 rat tissues into the adult rat; after each additional injection the immunity 

 of the host became more pronounced. On the other hand, Paula Freund 

 noted that a first unsuccessful subcutaneous inoculation of embryonal tissue 

 in the rat did not need to prevent the growth of a second intraperitoneal graft. 

 As in the case of active tumor immunity, we have not, in these experiments 

 with embryonal tissue, to deal with a specific immunity to the particular 

 homoiodifferential of the tissue which was used for immunization, since an 

 immunity to all embryonal tissues of the same species seem to have resulted 

 from the repeated injections. However, there is still the possibility that in 



