CHOKION WITH AMNION. 71 



That a severe endometritis might not result in thickening by fibrous prolif- 

 eration of the fetal membranes is well illustrated by No. 922, in which both mem- 

 branes were extremely thin, especially as compared to their size, although the 

 infection of the endometrium was severe. 



The resistance to infection, especially, perhaps, of young conceptuses, seems 

 very striking and recalls the experimental work of Maffuci (1894), but the ap- 

 parent failure of the tissues of young conceptuses to react toward infection as do 

 the tissues of the maternal organism is still more striking. However, this apparent 

 absence of defensive proliferative reactions on the part of embryonic tissues may 

 be due partly to the immaturity and the inadequately differentiated nature of 

 some of the tissues. 



In two specimens included in this group (Nos. 651e and 682), Mall found 

 remnants of the yolk-sac and the cord respectively; and in No. 645 also an epithelium- 

 lined cavity in the chorionic membrane, probably allantoic in origin. The presence 

 of these structures did not, however, affect the classification of the respective 

 chorionic vesicles. Nevertheless, these observations are interesting because, like 

 other similar observations previously mentioned, they indicate that the yolk-sac and 

 a portion of the cord or the allantoic stalk may persist even after the destruction 

 of the amnion and embryo has become complete. That the embryo and amnion 

 disintegrate relatively easily was emphasized also by Mall (1908). 



The amniotic conditions in some of the specimens of this group seem to imply 

 a growth of the chorionic vesicle after the death of both embryo and amnion. 

 Since the early amnion is related very intimately to the embryo, and since its 

 growth probably is very largely dependent upon the maintenance of the normal 

 composition of the amniotic fluid, a slightly continued growth of the chorion would 

 seem to be not improbable. But since the composition of the amniotic fluid must 

 change soon after the death of the embryo, it is probable that such an exceedingly 

 delicate and non-vascular structure as the amnion can not long survive. None 

 of these things is true, however, of the chorion, which often retains its connection 

 with its nutritive supply through the fastening villi, and hence is not seriously 

 affected at once by the degenerative changes within the contained vessels. In- 

 stances in which the amniotic vesicle is only a fraction say one-fifth or even one- 

 eighth as large as the chorionic vesicle, are not very rare, and others in which, at 

 the time of abortion, the relative proportions of these membranes are wholly unlike 

 the normal, are not uncommon. In one instance, for example (No. 1962), which 

 came under my direct observation, the dimensions of the chorionic vesicle were 

 61 by 44 by 34 mm., but the largest diameter of the slightly collapsed amnion was 

 only 19 mm. In this case the peri-amniotic and intra-amniotic fluids were entirely 

 normal in gross appearance and contained no suspended matter whatever. The 

 embryo was detached but intact and was represented by a small irregular nodule 

 3.5 mm. long. From this it will be seen that although the amnion was relatively 

 too large for the embryo, it nevertheless was too small for the chorion. That the 

 small size of the amnion was not due to retraction seems to be indicated by the 

 absence of any thickening in its walls. Indeed, the latter were entirely transparent, 



