MOTHER-FOETUS RELATIONSHIP I25 



(often appearing in the author's colony) has not been investigated, 

 the effect of some abortive pregnancies could not be excluded. 



In our laboratory, the experiments of Prehn were repeated 

 (with a different line of C57BL mice — H-2^) using a better defined 

 control. This consisted of matings between normal fertile males 

 and sterile females; female sterility was produced by irradiating 

 virgin females with two doses of 300 r. each at an interval of 2 

 weeks. After disappearance of cyclic vaginal cornification one 

 isologous ovary was transplanted subcutaneously to these 

 sterilized animals to restore the hormonal function since otherwise 

 the females would not have mated. Under these conditions, the 

 effect of insemination could be dissociated from that of the 

 pregnancy. The effect of pregnancy was studied in females caged 

 together with males (2 $ + i (J in one cage) to produce as frequent 

 Utters as possible. The litters were always discarded and approxi- 

 mately 2 months after the last Utter females were grafted with 

 isologous male skin using the usual technique. Bandages were 

 removed on the loth day and daily gross examinations were made 

 until the grafts were rejected. 



Experimental results are summarized in Table III. It can be 

 seen that three or four prior pregnancies caused a highly significant 

 prolongation of the survival time of male skin grafts transplanted 

 to multiparous females; 23 out of 31 grafts were rejected (with a 

 mean survival time of 33 ± 5*7 days) whereas 8 of them still 

 survived 50 days after transplantation. Even in females which 

 had experienced two pregnancies only (4 animals) the male-graft 

 survival-time was significantly prolonged (26 ± 3-4 days). 

 There was no significant difference between this value and that of 

 25 male skin grafts rejected by sterile mating females; in this 

 control group, however, 3 grafts were still in place 36 days after 

 transplantation. 



This implies that even mating itself leads to a significant 

 prolongation of male skin survival time in the nulUparous females, 

 comparable with the effect of two prior pregnancies. Other 



