7 2 



Scientific Proceedings (36). 



vascularized ; yet if she still carries young, it does not grow. On 

 the other hand, it does not die, as it would in an unfavorable alien 

 host. The fragments remain in good health for a considerable 

 period. At the end of seven days the thin strand of grafted tissue 

 consists of minute bits of cartilage, nests of epithelium, and a con- 

 nective-tissue of embryonic type, all with little sign of degener- 

 ation ; whereas in the hysterectomized mother the nodule that has 

 already developed is made up of relatively large masses of cartil- 

 age, epithelial cysts distended with secretion or cast-off cells, and 

 a connective tissue approaching the adult in type. Many signs 

 of beginning degeneration are seen, in the cartilage especially. 



These facts have a considerable bearing on tumor problems, 

 especially on Ehrlich's hypothesis of immunity by atrepsia — im- 

 munity by the lack of a specific food substance. Ehrlich holds 

 that a specific " X substance " is necessary to tumor growth 

 because (1) mouse tumor when introduced into rats grows for a 

 short period only and then retrogresses, — presumably for lack of 

 the "X substance," and (2) because the presence of a large, rapidly 

 growing tumor in a mouse prevents (by its utilization of " X sub- 

 stance ") the development of other grafts in the same animal. But 

 in view of the experiments just detailed, it must be granted that, if 

 tumor requires an " X substance," so developing embryo requires a 

 " Y substance." For (1) mouse embryo when implanted in rats 

 grows for a brief period and then retrogresses, 2 and (2) the pres- 

 ence of a developing litter in utero prevents the growth of embryo 

 grafts. 



But the question may well be asked whether one need suppose 

 for the growth of tumor or embryo the presence of special sub- 

 stances other than the circulating food required by mouse-tissue 

 in general. A lack of this might well explain the ultimate failure 

 of grafts in the rat, and its total utilization this failure when the 

 host-mouse already carries a rapidly growing tumor or a litter of 

 developing embryos. It should also be recalled that numerous 

 observers have found pregnancy of the host to interfere with the 

 growth of implanted tumors. 



2 Loc. cit. 



