LYSIS AND RESORPTION OF CONCEPTUSES. 279 



resistance on its part than that possessed by either amnion or chorion, or to a 

 preponderance of enzymes within it. Autolysis of the body of the embryo before 

 that of the membranes may also be due to the fact that the adnexa, especially the 

 chorion, or at least parts of it, often preserve vitality long after the death of the 

 embryo because of its direct relation to the uterus. Nevertheless, it often is 

 surprising how long the form of a small retained fetus, or even of the amnion, has 

 apparently been preserved, although it should be remembered that in some cases 

 the preservation of external form gives little indication of the true state of the 

 constituent tissues. If the advent of proteolytic fat- and carbohydrate-splitting 

 enzymes in fetal tissues is gradual, the surprisingly long time during which some 

 of the small embryos are preserved may be due to a considerable degree to this fact. 

 Jones and Austrian (1907) found, for example, that the liver of a young pig embryo 

 contains no nuclein enzymes, but that these increase as fetal development pro- 

 ceeds. The latter finding seems to be confirmed also by data given by Mendel 

 and Leavenworth (1908), although these investigators found enzymes present at 

 all ages. Schlesinger (1903) , who was, I believe, the first to establish the occurrence 

 of autolysis in retained human fetuses, also found that the rate of autolysis varied 

 with age and other conditions. 



Since the chorionic villi do not undergo autolysis first, the conclusion that 

 heterolysis is not an important factor in lysis of the conceptus also seems justified. 

 If enzymes of decidual origin played any large part in the process of lysis of the 

 conceptus, one might, I presume, expect to find instances in which at least portions 

 of the chorionic vesicle underwent lysis, although the embryo itself remained quite 

 unaffected. This, however, never seems to be the case, and the same thing holds 

 for the placenta and the chorionic vesicle and also for the decidua. That heterolysis 

 probably plays only a very subsidiary role is indicated also by the fact that autol- 

 ysis takes place in tubal implantations as well, and still more convincingly by its 

 occurrence in ovarian implantations, as illustrated especially by the case of Holland 

 (1911) and by other cases referred to by Meyer and Wynne (1919), in which the 

 escape of portions of the conceptus from the ovarian implantation cavity could be 

 wholly excluded. One reason for prolonged preservation of the decidua no doubt 

 lies in the fact that it as a whole, or at least in large part, retains vitality because 

 it remains quite undisturbed in its vascular relations. 



