394 THE PHYSIOLOGY OF REPRODUCTION 



vast amount of work done in the first half of the nineteenth century. 

 John Hunter l stated that the maternal blood circulated through the 

 placenta, and this view, which, according to Waldeyer, 2 had formerly 

 been held by Yater and Noortwyk, though the latter at least believed 

 in the communication of the maternal and foetal circulations, was 

 supported by the subsequent dissection of injected placentae by 

 John Hunter and his brother. The statement of the former that 

 " the blood of the placenta is detached from the common circulation 

 of the mother, moves through the placenta, and is then returned 

 back into the circulation of the mother," gave rise later to a consider- 

 able amount of discussion. They showed that the decidua was uterine 

 and not foatal, and the decidua reflexa was first figured in one of 

 William Hunter's plates. 3 



It is remarkable that John Hunter did not recognise the placenta 

 as the organ of foetal respiration. A century before, Mayow 4 had 

 declared that the placenta functioned as a foetal lung, the umbilical 

 vessels taking up the nitro-aerial gas (oxygen) and carrying it to the 

 foatift. This view was adopted by Ray, 5 who compared the villi lying 

 in the maternal sinuses to the gills of a fish in the water. The first 

 to take up Priestley's discovery of oxygen, and state definitely that it 

 was oxygen that went constantly from mother to foatus, and whose 

 absence caused foetal asphyxia, was Girtanner in 1794. But all 

 doubt was not removed till, in 1874, the spectroscopic bands of 

 oxyhsemoglobin were demonstrated in the umbilical vein of a guinea- 

 pig by Albert Schmidt, a pupil of Preyer. 6 



The work of the brothers Hunter was carried on by Weber,. 

 Goodsir, Coste, Eschricht, Reid, and others. Of the many investiga- 

 tions, none had such an important influence as the researches of 

 Goodsir. 7 He first studied the placental cells with regard to their 

 function, His predecessors had spoken in the vaguest terms of the 

 passage of nutriment from mother to foetus, but Goodsir had definite 

 ideas. He described the villi as having two covering layers of cells, 

 an external system belonging to the decidua, and an internal belonging 

 to the chorion. As to their function, he says : " The external cells 

 separate from the blood of the mother the matter destined for the 

 blood of the foetus they are secreting ; the internal cells absorb the 

 matter secreted by the agency of the external cells." Thus we have 



1 Hunter (J.), Observations on Certain Parts of the Animal Economy, Edit, by 

 Palmer, vol. iv. 



2 Waldeyer, " Bemerkungen liber den Ban der Menschen- und Affen- 

 placenta," Arch. f. mikr. Anat., vol. xxxv., 1890. 



3 Hunter (W.), Anatomy of the Human G'ravid Uterus, Birmingham, 1777. 



4 Mayow, Tractus Tertius de Respirationc Foetus in Utero, 1674. 



5 Ray, The Wisdom of God in the Creation, lath Edition, 1754. 

 See Preyer's Specielle Physiologie des Embryo, 1883. 



7 Goodsir, Anatomical and Pathological Observations, Edinburgh, 1845. 



