FETUS COMPRESSUS. 99 



His (1882, 1891) found 22 per cent of 62 aborted specimens pathologic, and 

 J. Kollman (1889) stated that it is generally known that one-half of all abortuses 

 are pathologic. Giacomini (1894) claimed that as many as 80 per cent of all abortuses 

 are abnormal, and Phisalix (1890) declared that normal specimens are rare among 

 abortuses; but Mall (1917) found only 39.6 per cent pathologic conceptuses among 

 the first 1,000 accessions in the Carnegie Embryological Collection. However, 

 cyemata classed as pathologic formed only 26.8 per cent among these accessions, 

 the rest being composed merely of vesicles classed as pathologic. 



Because of the presence of certain changes in the chorionic vesicle, Crosti 

 (1896) concluded that the cause of abortion is primary in the vesicles. Giacomini 

 (1894) declared, however, that it was impossible to decide whether the change 

 noticed by him was primary or secondary, and emphasized particularly that 

 the decidua should be studied because of its great influence on early develop- 

 ment. His (1882) concluded that all abortive forms are primary, but later (1891) 

 decided in favor of a secondary origin, a view held also by Mall (1917 C ). One 

 would hardly seem justified in assuming, however, that all cyemic abnormalities 

 or malformations are secondary in origin, for such an assumption would completely 

 ignore or deny the existence of true hereditary anomalies such as polydactyly, 

 hyperphalangism, etc. However, the mere possibility of the occurrence of anoma- 

 lies of secondary origin makes the identification of these extremely desirable and 

 important, although some of the achievements of experimental teratology seem to 

 suggest that it may remain impossible to distinguish between anomalies which are 

 primary and those which are secondary in origin. 



Since the extension of our knowledge of the subject of human embryology 

 necessarily has been from the older to the younger, it was inevitable that atten- 

 tion should be first directed especially to placental changes. Hence the literature 

 upon the subject of placental pathology is extensive, while that upon the pathology 

 of the cyema and chorion and also upon the decidua is small or even fragmentary. 

 However, now that our knowledge of extremely early conceptuses is being extended 

 much more rapidly, we soon shall be able to recognize the normal with more 

 certainty, which alone will be a great step in advance. 



Giacomini (1894) stated that many observers have noticed that abnormal 

 changes arise in the membranes as soon as the development of the embryo is 

 interfered with. He described these changes as the formation of vesicle-like 

 structures in relation to both amnion and chorion. 



A very interesting question is that of the invasion of the conceptus by cells 

 of maternal origin. As long as the chorionic epithelium remains intact I never 

 have seen any evidence of it, not even in the stroma of villi which were directly 

 in contact with an abscess. These observations also are in accord with those of 

 Nattan-Larrier and Brindeau (1905 b ). Nor have I ever seen anything suggesting 

 direct invasion of the fetal circulation by cells from the maternal circulation. 

 When one recalls the intimate relationship of the two circulations, it is surprising 

 that such an invasion does not occur, for it would seem to be especially easy, but 

 it is only after the chorionic epithelium is destroyed that maternal leucocytes seem 



