the Physiology of the Egg. 307 



change in its chemica] constitution, I instituted the followino- 

 experiments ; viz. 



Experiment 1. 

 Twenty-one hen's eggs newly laid, when punctured at their 

 obtuse extremity, yielded only 1 cubical inch of gas, which, when 

 received in a jar, and subjected to the eudiometric test of 

 Dr. Priestley, I found to be pure atmospherical air. 



Experiment 3. • 

 Two eggs, after 20 days' incubation, were opened under the 

 surface of water, from which 1 cubical inch of gas was collected: 

 this I also discovered to be atmospherical air, contaminated how- 

 ever with a small portion of carbonic acid, which I suspect to be 

 derived from the venous blood of the chick, and which seems to 

 establish another most beautiful analogy betiveen this mode of 

 oxygenation, and respiration after birth. 



From these results the following corollaries may be drawn : viz. 



1. The foUiciilus aeris before incubation contains atmosphe- 



rical air. 



2. No other chemical change takes place in the constitution of 



the air, than a small inquination Avith carbonic acid. 

 5. It gains by incubation an increase of volume, which takes 

 place nearly in the ratio of 10 to 1. 



I must here remark, that its extent docs not increase equally 

 in equal successive portions of time, but observes a rate of pro- 

 gression, which is accelerated as the latter stages of incubation 

 advance : it seems, however, to arrive at its maximum of dilatation 

 a few days previous to the exclusion of the animal. 



In the eggs of inferior animals, the embryon does not appear- 

 to be oxygenated by any distinct apparatus, but, like the animal 



which 



