On the Respiration of the Foetns^ etc, 217 



almost infinite number of little bubbles and into a 

 much greater bulk than before, a sufficiently clear 

 proof that certain aerial particles are most intimately- 

 mixed with these liquids. To which I add that the 

 humours of an Qgg when thrown into the fire, give 

 out a succession of explosive cracks, which seem to be 

 caused by the air particles rarefied and violently 

 bursting through the barriers which confined them. 

 And hence it is that the fluids of an Qgg are possessed 

 of so fermentative a nature. For it is indeed prob- 

 able that the spermatic portions of the uterus and its 

 carunculae are naturally adapted for separating aerial 

 particles from arterial blood. 



These observations premised, we maintain that the 

 blood of the embryo, conveyed by the umbilical 

 arteries to the placenta or uterine carunculae, brings 

 not onl}^ nutritious juice, but along with this a portion 

 of nitro-aerial particles to the foetus for its support ; 

 so that it seems that the blood of the infant is 

 impregnated with nitro-aerial particles by its circula- 

 tion in the umbilical vessels, quite in the same way as 

 in the pulmonary vessels. And therefore I think that 

 the placenta should no longer be called a uterine liver 

 but rather a uterine lung. 



Should any one object here that such a mode of 

 breathing in the uterus could be carried on without 

 umbilical arteries, since it would suffice if the 

 nutritious juice were to pass, charged with nitro-aerial 

 particles, to the foetus through the umbilical vein, I 

 answer that to supply the part of respiration there is 

 need of a continuous supply of air, but that the 

 nutritious juice should not be in such abundance as to 

 come to the child in a perpetual stream, and therefore 

 it is necessary that the umbilical arteries should be 

 so formed, that the arterial blood, continuously sent 



