On the Respiration of the Foetus^ etc. 223 



membrane, but I have ascertained that the shell of 



the egg is everywhere lined by the first membrane 



and that the cavity lies between the two membranes. 



With regard to the purpose served by the air 



contained in this cavity, I cannot agree with the 



learned Fabricius who maintains that air is stored in 



it for the respiration of the chick ; for there is so 



little of it that it would barely suffice for once 



starting respiration. Besides, the air enclosed in the 



cavity is completely shut out from the foetus by the 



intervening membrane, so that it cannot pass to the 



foetus for the purpose of respiration, as will be evident 



from the following experiment. For let the sharper 



end of an Qgg be so broken that its fluids can be 



poured out in order that the said cavity may be seen, 



which in eggs that are not yet hatched will be very 



small. Then let the Qgg be put into a glass and the 



air pumped out by Boyle's pump. 



When this is done the small portion of air con- 

 tained in the cavity will at once expand when the 

 pressure of the atmosphere is withdrawn, in virtue of 

 its elastic force, and will push forward the membrane 

 covering it a long way, so that the cavity will enlarge 

 to half the size of the egg, more or less. Nay, the air 

 sometimes by separating the said membrane from the 

 other to which it was previously attached, will push it 

 beyond the cavity of the egg. And from this we may 

 infer that the air cannot pass through the lining 

 membrane and be conveyed to the chick, for if it did, 

 this membrane would not be pushed so far by the 

 enclosed air nor become distended. 



But since that air within the egg cannot reach the 

 chick for the function of respiration, let us inquire 

 what purpose it serves. For it is by no means to be 

 believed that the air which Nature has so carefully 



