720 THE RESPIRATION AND [pt. iii 



instead of an air-space as the egg and the oviduct slowly cooled. And 

 by clipping a window in the uterine wall, he could produce it at will 

 at any part of the egg. The analogous air-space in the cocoon of 

 the silkworm has been studied by Portier & de Rorthays, who found 

 that carbon dioxide accumulates in it as metamorphosis proceeds, 

 just as during development in the hen's egg. Dubois and Dubois 

 & Couvreur have also studied this air-space. 



In the course of his respiration experiments, Hasselbalch investi- 

 gated the contents of the air-space, obtaining figures as follows : 



Days after 

 fertilisation 



2 



5 



Infertile 



Hasselbalch was naturally very interested that the fertile eggs seemed 

 to have slightly more oxygen in their air-spaces than ordinary air, 

 in view of his other researches on the oxygen production of the 

 birds' egg during the first few days. The fact that he got normal 

 figures for infertile eggs still further contributed to that conclusion. 

 But the classical work on the subject is that of Aggazzotti, who in 

 1 9 14 measured the percentage of oxygen and carbon dioxide in the 

 air-spaces of incubating eggs, not only at sea level but at the mountain 

 experimental station of Col d'Olen. 



Taking first the normal figures, Aggazzotti found that in fresh eggs 

 the carbon dioxide content of the air-space is high, from 1-42 to 

 2-05 per cent., while the oxygen content is just equivalent to that of 

 the external air, though it may be very slightly above it (20-72 to 

 21-29 per cent.). The former fact agrees excellently with the pre- 

 liminary output of carbon dioxide (due to the oviduct), which so 

 many workers have observed, and perhaps the latter fact may be 

 taken as confirmation of Hasselbalch's statements about oxygen 

 production. After 8 or 9 hours, however, the carbon dioxide has 

 fallen to o-6 per cent., while the oxygen has remained stationary, 



J 



