96 



blood thus receives perfects the organic spirit, or an essential 

 part of it, residing in some organ of the foetus, further related 

 with its diffused spirit. As oxygen, as is proved, is capable of 

 producing a similar change in the blood, it is to be considered 

 whether these properties, originally conferred in the same manner 

 as the other properties of the ovum, are identical with oxygen. 



85. Oxygen, unassisted by any vital properties resident in 

 the textures, is capable of producing the change of colour men- 

 tioned, but whether it furnishes by itself the properties essential 

 to life, or whether the blood is fitted for this purpose by proper- 

 ties of oxygen, conjoined with those resident in the textures, is a 

 point upon which we have no direct testimony; because, when 

 life is extinct in the lungs it is extinct elsewhere, and therefore 

 its relation with mere oxygen cannot be ascertained. 



86. But that oxygen is the identical influence which is con- 

 ferred on the blood in the placenta appears probable. The evi- 

 dence in its favour is that atmospherical oxygen will produce that 

 change in blood which fits it for the purpose of remote vitality. 

 The truth of this conclusion is to be known only by ascertaining 

 whether the properties productive of change of colour in the 

 blood, and those endowing it with a cause of vitality, belong 

 wholly to oxygen. The affirmative is indicated, and only indi- 

 cated, by the known importance of oxygen in respiration: and as 

 there is not even an indication to the contrary, we may presume 

 that the portion of the ovum which forms the placenta contains 

 oxygen in alliance with other properties of life. 



87. This view of the matter being thus far granted, another, 

 before exhibited, will with propriety be opposed to it. Supposing 

 oxygen to have been originally in alliance with that part or 

 sphere of the organic spirit destined to form the placenta, the 

 quantity of this oxygen must be exceedingly small, not sufficient 

 for one round of circulation, in the latter stages of foetal existence; 

 and as it is confessed that there is no source of oxygen by atmos- 

 pherical communication, in what manner is the oxygen obtained 

 which is said to be possessed by the placenta, or how is this small 

 quantity of oxygen (supposing such original quantity to exist) so 

 greatly increased? This objection is well urged, and the explanation 

 will extend a little our inquiries into these mysterious processes. 



88. It is obviously necessary that t'he increase of oxygen 

 should be in a ratio to the increase of blood. As the source of 

 this oxygen is not from without, it must be internal. The only 

 internal source of oxygen is that which is also the only source of 

 the organic materials, the fluids obtained from the matter. 



89. To imagine that venous foetal blood in the placenta be- 

 comes oxygenated by mixture of fluids derived from the mother 

 would be to suppose, 1st, a readier communication between the 

 foetus and the uterus than we have reason to believe ; and, 2nd, a 

 rapidity of nutrition (or repletion) would thus be occasioned which 

 does not correspond with the ratio of visible growth. 



