On the Respiration of the Fcetus, etc. 219 



regard to this it is probable that the primogenial 

 liquids of the egg (which, as has been already shown, 

 abound with aerial matter), continuously brought by 

 the umbilical vessels to the chick, perform for it the 

 part of not only of nutrition but also of respiration, 

 just as is done in the uterus. 



If any one shall here object that there is not so 

 much air contained in the egg as is required to supply 

 the want of respiration during the -vyhole period of 

 incubation, I answer that the air stored in the ^g'g is 

 not common air but is that aerial something which is 

 separated from common air by the action of the lungs. 

 Indeed, of the air which we inhale it is only a very 

 small portion that is transmitted into the mass of the 

 blood ; what remains of the air is expelled in ex- 

 piration as being useless. But what there is of air, 

 pure and vital (such as we are to suppose contained in 

 the ^gg)^ may be compared and held to be equal to a 

 great quantity of common air. 



Nor is it to be forgotten that the foetus in the egg 

 and in the uterus makes but the very smallest 

 expenditure of nitro-aerial particles ; for these are 

 mostly required for muscular contraction and for 

 carrying on the concoctions in the viscera, as we shall 

 elsewhere show. Hence, according as any one 

 exercises himself more or less, so he has need of a 

 more intense, or of only a more moderate respiration. 

 And undoubtedly in drowsy affections, in which the 

 animal functions are almost suspended, respiration 

 seems to be all but suppressed. Wherefore, as the 

 foetus in the uterus and in the Qgg keeps holiday from 

 nearly every movement except that of the heart, a 

 smaller ration of nitro-aerial particles from the arterial 

 blood of the mother, or from the fluids of the Qgg^ 

 abundantly suffices for its requirements. 



