2 Dr. Paris on the Physiology of the Egg. [July, 



principle, which thus establishes an important relation between 

 the diminution of the bulk of the ovular contents and the extent 

 of this pneumatic apparatus. During the progress of incubation, 

 it is dilated to a very considerable magnitude. Its uses seem 

 to have been first understood and appreciated by Harvey : 

 " Utilis est ad ovi ventilationem, ac Pulli perspirationem, refrige- 

 rium, et respirationem, ac denique ad loquelam, unde cavitas ilia 

 primo exigua, mox major, ac denique maxima eouspicitur, prout 

 variijam nempe dicti usus post ulaver int." 



Very early after incubation, the cieatricula expands into- 

 several circles, containing an ash-coloured fluid, called by 

 Harvey " colliquamentum " in this, on the fourth day, theheart, 

 like a vibrating point, " punctum salieus" for the first time, 

 becomes visible, and blood-vessels are seen defining, like a 

 frino-e, the cieatricula ; these meatus venales, which are hereafter 

 to become the umbilical vessels, extend and multiply their rami- 

 fications on the yelk and white, by which the blood is exposed 

 to the action of the air in the follicle, oxygenated, and returned 

 to the embryon : to establish, however, this theory upon a solid 

 basis, it became necessary to discover the nature of the air that 

 inflates the follicle, and which has hitherto remained unexamined. 

 We are informed by Buffon, that it is a product of the fermenta- 

 tion which the different parts of the egg undergo. If the Count's 

 conjecture be substantiated, the gas must be no?i-respirable : to 

 determine this point, and to discover whether the process of 

 incubation produces any change in its chemical constitution, I 

 instituted the following experiments : 



Experiment 1. — Twenty-one hens' eggs newly laid, when 

 broken under the surface of water, yielded only one cubical inch 

 of gas : this, when received in a jar, and subjected to an eudio- 

 jnetric test, proved to be pure atmospheric aiF. 



Experiment 2. — Two eggs, after 20 days' incubation, were 

 opened as before, when one cubic inch of gas was collected, which 

 I also discovered to be atmospheric air, contaminated, however, 

 with a portion of carbonic acid. This latter gas I suspect to be 

 derived from the venous blood of the chick, which seems to esta- 

 blish another analogy between this mode of oxygenation and 

 respiration after birth.* From these results, the following corol- 

 laries may be drawn : 1 . The folliculus aeris contains before 

 incubation atmospheric air.f 2. No other chemical change is. 

 effected in its constitution than a small inquination with carbonic 

 acid. 3. It gains by incubation an increase of volume, which 



• As in respiration, may not this combination of oxygen with the blood generate 

 heat ? For Mr. Hunter's experiments prove that there is a difference of several degree* 

 in the temperature of an addled egg, and in that of one advanced in its evolution, 

 although they have both been alike subjected to the animal heat of incubation. 



"t" By the application of heat this air is expanded, and, if suddenly, it will burst the 

 shell, and scatter the contents; the obtuse extremity should, therefore, be alway* 

 pricked with a pin before the egg is roasted, a fact well known to the country housa- 

 wifei andhence the old adage, " There it rcaum in /vesting an egg." 



