CHAPTEK XI 

 t 



FCETAL 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 (more's 

 the pity) with nota few."^— Samuel ButI/ER. 



PART I 



THE PLACENTA AS AN ORGAN OF NUTEITION 



I. Historical Survet 



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 diligent observation. But 

 for a century after his death the placenta received little notice. 

 With the introduction of the microscope 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. 



In the second half of the eighteenth century were published the 

 researches of John and William Hunter on the human placenta, 

 important not , only in themselves, but as destined to set agoing the 



' By James Lochhead. 



2 Harvey, Tke Generation of Animals, London, 1651. 



13 A 393 



