the Physiology of the Egg. 307 
change in its chemical constitution, I instituted the following 
experiments ; viz. 
EXPERIMENT 1l. 
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 2. 
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 between. this mode of 
oxygenation, and respiration after birth. 
From these results the following corollaries may be drawn: viz. 
1. The folliculus acris before incubation contains atmosphe- 
rical air. 
.9. No other chemical cte takes place in the constitution of: 
the air, than a small inquination with carbonic acid. 
5. It gains by incubation an increase of volume, which takes. 
| place nearly i in the ratio of 10 to 1. 
_I must here remark, pt its extent does ot: 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. 
