2 1 6 Mayow 



doubted that the vena cava also exists from the very 

 commencement of life. For why should not Nature 

 be as ready to form the vena cava as that long circuit 

 of umbilical vessels which are quite useless after birth 

 and have to be destroyed ? 



Wherefore, since the functions hitherto assigned to 

 the umbilical arteries do not appear to be suitable and 

 real, we may hold with divine old Hippocrates that 

 in the embryo the umbilicus supplies the place of 

 respiration, which is also the opinion of the learned 

 Everard. 



But I cannot agree with Everard in the reason he 

 assigns for setting up respiration in the uterus. For 

 this learned man thinks that the blood of the infant is 

 conveyed through the^ long circuit of the umbilical 

 vessels in order that it may be cooled in its journey. 

 But indeed it is by no means to be believed that such 

 a cooling of the blood takes place in the very warm 

 uterus. And even though there were such cooling, it 

 would serve in no way the purpose of respiration, for, 

 as we have shown elsewhere, this contributes rather 

 to the heating than to the cooling of the blood. 



But now that we may prepare the way for our 

 opinion as to respiration in the uterus, we observe, in 

 the first place, that it is probable that the albuminous 

 juice exuding from the impregnated uterus is stored 

 with no small abundance of aerial substance, as may 

 be inferred from its white colour and frothy character. 

 And in further indication of this, the primogenial 

 juices of the ^gg^ which have a great resemblance 

 to the seminal juice of the uterus, appear to abound 

 in air particles. For if the white or the yolk of an 

 ^gg be put in a glass from which the air is exhausted 

 by means of Boyle's pump, these liquids will im- 

 mediately become very frothy and swell into an 



