358 THE PHYSIOLOGY OF REPRODUCTION 



In the second half of the eighteenth . century were pub- 

 lished the researches of John and William Hunter on the human 

 placenta, important not only in themselves, but as destined 

 to set agoing the 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 Vater 

 and Noortwyk, though the latter at least believed in the com- 

 munication of the maternal and foetal circulations, was sup- 

 ported 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 considerable amount of discussion. They showed 

 that the decidua was uterine and not foetal, 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 foetus. 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 foetus, and whose absence 

 caused foetal asphyxia, was Girtanner 6 in 1794. But all doubt 

 was not removed till, in 1874, the spectroscopic bands of oxy- 

 haemoglobin 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 

 investigations, none had such an important influence as the 



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

 by Palmer, vol. iv. 



2 Waldeyer, " Bemerkungen iiber den Bau der Menscben- und Affen- 

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



3 W. Hunter, Anatomy of the Human Gravid Uterus, Birmingham, 1777. 



4 Mayow, Tractus Tertius de Respiratione Fostus in Utero, 1674. 



5 Ray, The Wisdom of God in the Creation, 12th Edit., 1754. 

 See Preyer's Speciette Physiologic des Embryo, 1883. 



