THE INCUBATION OF HENS' EGOS 209 



Nature. During the time that a setting lien is away from her 

 nest for tlie purpose of feeding the eggs become more or 

 less cooL Because this happens in Nature it is assumed tliat 

 hotter hatches will result if the eggs are cooled wlien arti- 

 ficially incubated. 



There are two reasons given why cooling strengthens the 

 hatching power of eggs. It is argued that just as ])ersons, 

 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 tem])erature of inculca- 

 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. 



Atwood' suggests that "as chick embryos l)chave iiki' cold- 

 blooded animals, reducing the temperature of the egt;' de- 

 creases the vital acti\'ity and it is difficult to conceive any 

 valid reason for slowing down this activity." 



Larason- compared cooling and not cooling, keeping 

 keeping records on between six and se\'en thousand eggs. 

 "The cooling method was to liegin cooling on the third day 

 and cool each night and morning for five minutes, then the 

 following day the time A\as increased one minute and so on 

 until the eighteenth day." 



Sixty-seven per cent of the fertile eggs hatchcfi in the 

 incubators which were cooled and 70 ])er cent of the fertile 

 eggs hatched where they were not cooled. 



Five hundred chicks, half of which had been cooled 

 (luring incubation, and half not cooled, were watched for the 

 first four weeks during which 34 chicks died. Twenty 

 were from the cooled eggs and 14 from the uncooled. 



ITe further found that eggs from strong stock would stand 

 from four to five hours at 50^ F. after the first twenty-four 

 hours of incubation From this point on the time could 

 be increased up to fifteen hours on the tenth to twelfth days. 



1 West Virtfinia Circular, No. 25. 



" Jour. Am. .\ssn. Inst, and Invest. Poul. Husli., vol. iv, No. 5. 



14 



