INCUBATION OF THE EGG OF THE COMMON FOWL. 3/1 



mentally affects the growth of the chick when there is an abun- 

 dant supply of fresh air. There is not the least doubt, however, 

 but what it has a beneficial influence in cases of poor ventilation, 

 and since no incubator is supplied with too much, it probably is 

 best to adopt the common practice of cooling the eggs. In so 

 doing it would not seem advisable to cool the eggs for more than 

 twenty to thirty minutes each day, for the first fifteen or eighteen 



days. 



VI. VENTILATION OF EGGS. 



Natural ] Mutilation. - -In natural incubation a perfect ventila- 

 tion exists. An abundance of fresh air can always reach the 

 eggs by diffusing through the feathers which cover them. This 

 process is constantly going on during incubation, the foul air like- 

 wise having free exit. There is thus ample opportunity for a 

 continuous circulation of air, and there is every reason to believe 

 that it takes place. There is also afforded by the feathers a com- 

 plete barrier against sudden draughts of air. The fresh air is also 

 raised to a certain temperature through the heat of the hen before 

 it comes in contact with the eggs, which also serves to reduce any 

 excessive humidity. This perfect system of ventilation cannot 

 fail to impress one of its importance in facilitating the growth of 

 the chick. 



Dareste ('91, p. 150) conducted the following series of experi- 

 ments : All the apertures of the incubator were closed during in- 

 cubation, and upon examination it was found that nearly all the 

 embryos had died. It was found further, that there had developed 

 in the albumen a microscopic organism resembling the ordinary 

 yeast plant. The author concludes that air modified by embry- 

 onic respiration, facilitates the growth of parasitic organisms. 



Gerlach ('82, p. 115) found that by diminishing the quantity 

 of air during incubation, he could cause dwarfing of the embryo. 

 He then tried whether an increase in the size of the embryo could 

 be brought about by increasing the quantity of air. A part 

 of the shell was scraped very thin and placed in an incubator. 

 During the first two days the normal and modified eggs were 

 alike, but after that time the embryo in the scraped eggs devel- 

 oped at a remarkably rapid rate, nearly twice as fast as in normal 

 growth. 



