92 BIOLOGICAL DIAGNOSIS OF PREGNANCY 



To us these observations and views had this much 

 value : that they directed our attention to the fact that, 

 during pregnancy, the appearance of substances, 

 that were in harmony with the species but not with 

 the plasma, might be possible. If our view is correct, 

 that the animal organism sets free ferments of a 

 special kind, as soon as material that is in harmony 

 with the species, but not with the plasma, passes 

 into the blood, then it ought to be possible to demon- 

 strate the existence of such ferments during preg- 

 nancy. As, however, the ferments, as we know from 

 experience, disappear fourteen to twenty-one days 

 after the actual introduction of disharmonious sub- 

 stances, it was scarcely possible to expect that defen- 

 sive ferments should be met with during the whole 

 period of pregnancy. One had to experiment with a 

 great many cases, before striking that one in which 

 dissolution of the cells of the villi had just taken place. 



Experience, however, soon showed that the serum 

 of pregnant individuals always contains defensive 

 ferments which are directed against placenta 

 albumen. We cannot, therefore, maintain that the 

 tearing off of the epithelium of the chorionic villi is 

 the only cause of the appearance of the defensive 

 ferments. It must be remembered that even the 

 mare exhibits, during pregnancy, defensive ferments 

 which are directed against placenta albumen ; yet the 

 placenta of the mare is related to the circulation in 



