So8 THE PHYSIOLOGY OF REPRODUCTION 



however, says that the presence of hydrogen peroxide is not required, 



i.e. that the placenta acts as a direct oxidase. 



No glycolytic ferment is present in the placenta.^ 



A few ferment actions still remain — e.g. the removal of urea from 



arginin, the decomposition of uric acid, and the oxidation of purine 



bases — which have not yet been investigated in the placenta.^ 



V. General Consideeations of-Tcetal Nutbition and 

 THE Placenta 



A. T/ie Flan of Placental Formation 



The problems of foetal nutrition are not new problems. The}' 

 deal with the assimilation of organic and inorganic substances, and 

 their incorporation in the developing tissues. These phenomena are 

 made up of a series of chemical changes which must be studied 

 individually before we can hope to understand the final sum which 

 constitutes foetal metabolism, or the disturbances which constitute 

 foetal disease. Set in the path traversed by the materials on their 

 way to the new organism is the placenta, a complex organ composed 

 of specialised maternal elements and newly developed foetal elements. 

 Among the Monodelphia no uniform plan is observable in the 

 formation of the placenta, nor is it possible to trace each step in its 

 evolution. But Duval's conception of this temporary organ as a 

 maternal hsemorrhage surrounded by foetal elements, and Hubrecht's 

 discovery of such a type of placenta in a mammalian order which is 

 among the most archaic, lead to a change in the ideas of placental 

 classification. We can no longer depend on the shape of the placenta 

 or the characteristics of the after-birth, for an understanding of its 

 morphological or physiological features. Eather must we go back 

 to the phenomena to be observed in the uterine fixation of the 

 blastocyst, and even earlier in the preparation for that fixation. At 

 this stage we find two constant features, one maternal and the other 

 foetal. The maternal change consists of au epithelial, connective 

 tissue or endothelial proliferation, the trophospongia, which is 

 " specially intended for the fixation of the blastocyst." According 

 to Hubrecht, it degenerates into a symplasma when the fixation is 

 accompKshed and the foetal elements are in contact with circulating 

 maternal blood. But its degeneration is not completed at that stage. 

 Though individual cells may die, other cells are formed and take 

 their place, at least in man, throughout the greater part of pregnancy. 

 Moreover, the cells have other functions to perform. Whether or 

 not they act as a defence against the excessive penetration of the 



' It cannot yet be held as proved that glycolysis by ferment action occurs 

 at all in animals. 



^ For a further study of the ferment content of the placenta see above, p. 465. 



