CHAPTER X' 



FtETAL NUTRITION: THE PLACENTA 



" Birth ... is commonly considered as the point at which we begin 

 to live. More truly it is the point at which we leave off knowing how to 

 live. . . . Not but what before birth there have been unsettled convictions 

 (mere's the pity) with not a few." — Samuel Butlee. 



PART I 



THE PLACENTA AS AN ORGAN OF NUTRITION 



I. Historical Survey 



The mammalian ovum, in all except the Monotremata, is small 

 and does not contain a sufficient supply of nutriment for the 

 developing embryo. It is retained for a longer or shorter period 

 in the uterus, where, by special modifications of the uterine 

 mucosa and a part of the ovum, the placenta is formed, and a 

 transmission of nutriment from the mother to the embryo is 

 made possible. The changes in the maternal and embryonic 

 tissues vary greatly in the several orders, and even in groups of 

 the same order, but in all they are sufficiently complicated to 

 render their explanation a matter of great difficulty. It is 

 doubtful if any anatomical structure has given rise to keener or 

 more prolonged controversies than the placenta. 



We owe to Harvey ^ the conception of the placenta as an 

 organ elaborating from the maternal blood the aliment necessary 

 for the growth and development of the foetus. He was the first 

 to reject the " subtleties and fanciful conjectures " on embryonic 

 development, and to advocate and practise direct and dihgent 

 observation. But for a century after his death the placenta 

 received httle attention. With the introduction of the micro- 

 scope the attention of biologists was directed towards the origin 

 and development of the embryo, and it was then that the 

 ovarian vesicles and spermatozoa were first observed. 



' By James Loohhead. 



' Harvey, The Generation of Animals, London, 1651. 

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