208 POULTRY PRODUCTION \ 



better hatches will result if the eggs are cooled when arti- 

 ficially incubated. 



There are two reasons given why cooling strengthens the 

 hatching power of eggs. It is argued that just as persons, 

 even in cold weather, seek relief from the constant heat of 

 internal combustion by drinking cold water, so the embryo 

 needs relief from the continued high temperature of incuba- 

 tion. 



What would seem to be more reasonable is the suggestion 

 that by cooling, the contents of the egg contracts somewhat, 

 thus drawing fresh air through the pores of the shell for the 

 ever-increasing demands of the embryo. 



Experimental data on this point is quite limited and some- 

 what contradictory. Stewart and Atwood^ found that "In 

 using incubators that were well ventilated, with the average 

 maximum and minimum outside temperatures at 80° and 

 54.7° respectively, the chicks appeared stronger at the age 

 of three weeks when the eggs were not cooled. With incu- 

 bators that were poorly ventilated and operated at a time 

 when outside temperatures were very high the results as 

 to hatches were inconclusive. The chicks, however, from 

 the cooled eggs were materially stronger than the others, 

 . . . as fewer of them died." 



Eycleshymer'' reports observations on the length of time 

 that six hens left their nests during incubation and found 

 that the time averaged about thirty minutes for the first 

 eighteen days. The longest time a nest was left exposed 

 was an hour and twenty minutes and the shortest time was 

 twelve minutes. This variation seemed to be dependent 

 upon the ease with which the hens were able to find food and 

 satisfy their hunger. As the result of his observations, he 

 came to the conclusion that the natural "cooling of eggs 

 is due to the necessity of obtaining food, and in no way 

 fundamentally affects the growth of the chick where there is 

 an abundance 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 



' West Virginia Bulletin No. 124. 

 ' Biological Bulletin, May, 1907. 



