THE INCUBATION OF THE EGG 179 



Temperature for Holding Hatching Eggs. — The belief that 

 the earher the development, that is under way at the time of 

 laying, is checked the better are the chances of holding eggs 

 successfully for hatching, has led to the general practice 

 among poultrymen of gathering the eggs often during the 

 incubating season and putting them in a cool place. 



Edwards,^ as the result of a series of comprehensive experi- 

 ments, has fixed the physiologic zero of the hen's egg at a 

 temperature lying between 20° and 21° C. This is the practi- 

 cal equivalent of saying that an egg will start to incubate 

 at a temperature lying between 68° and 70° F., and that to 

 insure the complete checking of development, eggs must 

 be kept in a temperature below 68° F. Practical experience 

 seems to indicate that eggs held in a temperature that is 

 even as possible, lying between the limits of 55° and 65° F., 

 give best results. Just what the temperature is at which 

 eggs begin to show the effects of chilling has not been deter- 

 mined so far as the author is aware. The place most likely 

 to furnish the best holding condition is a cool, well-ventilated 

 cellar. 



Turning Hatching Eggs. — As already pointed out, the yolk, 

 with the germ spot uppermost, tends to float on the albumen. 

 It is prevented from coming in actual contact with the shell 

 membrane by the dense layer of albumen which surrounds 

 it. When left in the same position for a considerable time 

 a constant though gentle tendency upward parts the coat of 

 dense albumen and allows the germinal disc to come in 

 contact with the shell membrane. With evaporation 

 constantly taking place the tiny embryo becomes adhered 

 to the membrane and is destroyed. When the eggs are not 

 allowed to remain in the same position, but are turned 

 fairly frequently, a new point of contact is given, and more 

 albumen brought between the germ and the shell membrane. 



Jackson^ reports, as the result of experiment, that after 

 the first two weeks there was a distinct advantage in keeping 

 eggs on their side and turning daily over, keeping them in 



' American Journal of Physiology, vi, 35. 

 2 Pennsylvania Bulletin No. 120. 



