BIOLOGICAL DIAGNOSIS OF PREGNANCY 93 



such a way as to exclude the possibility of the cells 

 of the chorionic villi getting into the blood. 



How can we then explain the existence of the 

 defensive ferments during pregnancy ? It can only 

 be in very exceptional cases that they are produced by 

 the invasion of morphological elements. In most 

 cases it must be the result of the transfer of particular 

 bodies the constituents of particular cells, or the 

 products of their decomposition. It may be, of 

 course, that the extraordinarily active metabolic pro- 

 cesses, which arise at the junction of the maternal and 

 foetal organisms, result in an insufficient reduction 

 of many of the products of the cells of the placenta; 

 the metabolism, in short, overreaching itself through 

 its own rapidity. It is, however, also conceivable 

 that the cells themselves break up easily. 



The following view is probably the correct one. 

 The organism of the mother has at its disposal, up to 

 the appearance of pregnancy, a certain amount of cells 

 of a certain kind, which all harmonize, in their meta- 

 bolism, with each other. Now, with conception, 

 comes the appearance of an entirely new kind of 

 tissue, which has to perform particular duties. 

 Although the impregnated egg and the developing 

 placenta, with all its various cells, are in harmony 

 with the species, nevertheless the metabolism of all 

 these cells appears as something quite new and 

 strange to the complex of cells composing the 



