SECT. 3] AND EIGHTEENTH CENTURIES 171 



the air is exhausted by the Boyhan pump these liquids will imme- 

 diately become very frothy and swell up into an 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 

 tgg when thrown into the fire, give out a succession of explosive 

 cracks which seem to be caused by the air particles rarefying and 

 violently bursting through the barriers which confined them. Hence 

 it is that the fluids of the egg are possessed of so fermentative a nature. 

 For it is indeed probable 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 only 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 circulation through the umbilical 

 vessels quite in the same way as in the pulmonary vessels. And there- 

 fore I think that the placenta should no longer be called a uterine 

 liver but rather a uterine lung". These splendid words, informed by 

 so much insight and scientific acumen, show that, by the time of 

 Mayow, chemical embryology had definitely come into being. He died 

 at the early age of thirty-six, and we may well ponder how different 

 the subsequent course of this kind of study would have been if he had 

 lived a little longer. 



The second part of Mayow's treatise is concerned with respiration 

 in the hen's egg during its development, and it may be noted that 

 his observations on the air contained in the liquids before develop- 

 ment probably account for the facts which have been reported at 

 one time and another concerning an alleged anaerobic life of embryos 

 in early stages. Mayow is wrong in supposing that the gas which he 

 pumped out from white and yolk was purely "nitro-aerial", but he 

 shows the greatest good sense in his reminder that the amount of 

 nitro-aerial particles required by embryos must be comparatively 

 small owing to their small requirement for "muscular contraction 

 and visceral concoction". His remarks on the effect of heat on the 

 developing egg are not so clear as the remainder of the treatise, but 

 he seems to mean that the heat will disengage the nitro-aerial particles 

 from the liquids, and so aid in respiration, an idea which was later 



