116 Discussion 



are going to put the physiologists in a very tight spot (for technical 

 reasons). What we wish to know, ultimately, is the ability of the foetus 

 to survive under particular conditions and there we have to take into 

 account the whole placenta. Is that a reasonable proposition? 



Wislocki: I agree with you that the whole placenta should be taken 

 into account. Nevertheless, few physiologists are familiar with it in 

 its entirety or have taken cognizance of it. The entire placenta, in 

 various mammals, may be composed of several quite different placental 

 structures including some type of yolk-sac placenta, a chorioallantoic 

 placenta, and the membranous chorion. These may function suc- 

 cessively or concurrently, as the case may be. Some functions and 

 metabolic transfers may occur solely through one of these structures, 

 while others take place through some other one. In the human, which 

 has solely a chorioallantoic placenta, all physiological exchange must 

 take place through it, with the possible exception of some transfer 

 through the membranous chorion. 



Hamilton: Would Prof. Wislocki agree that both aspects must be 

 considered ; the thickness of the placental barrier and the whole extent 

 of the placental barrier? We have got to bear in mind, a thin layer of 

 very great extent or a thin layer of limited extent and a thicker layer of 

 very great extent. 



Wislocki: Well, it turns out that as more and more chemistry and 

 histochemistry and enzymic chemistry is done upon the placental 

 barrier that thickness alone, apparently, becomes less and less important 

 because so many of these processes of transfer are influenced by chemical 

 transfer rather than, as was thought previously but still entertained 

 in some quarters, that it is all a consideration of a semi-permeable 

 membrane. 



Jost: Prof. Wislocki yesterday raised the point of the relation between 

 the foetus and the placenta, and I myself am very interested in such 

 a question. To what extent does the foetal physiology have any 

 importance for placental evolution? Prof. Wislocki, have you any 

 information about those placentas which develop in the absence of the 

 foetus? It is quite easy to obtain a placenta without a foetus either by 

 removal of the foetus or, for instance, by castrating pregnant rats ; then, 

 quite often, the foetus dies and the placenta continues to grow. In such 

 castrated rats, the placentas seemed to me to be even larger than normal. 

 I was very curious to know what happens in such a placenta. 



Wislocki: No, I have not studied any such placentas. It would be 

 invaluable to investigate, cytologically and histologically, placentas 

 which develop in the absence of the foetus. Placentas accompanying 

 the experimentally induced condition of postmaturity in rabbits would 

 also be particularly interesting to study with reference to senescence, 

 the mechanisms of placental transfer and the synthesis of placental 

 hormones by the trophoblast. 



Huggett: Some years ago, Dr. Pritchard and I investigated the effects 

 of foetal death in the rat and we found that if the foetus was killed before 

 the 11th day then almost invariably the placenta was absorbed. If, 

 however, it was killed after the 11th day when the foetal mesoderm had 



