86 SOME RECENT EXPERIMENTS IN INCUBATION 



perform. Is it the hand that liberates the captive chick? Does it break 

 down the prison walls and give life and liberty to the prisoner? 



The experiments at the Guelph Station corroborate the Utah tests, 

 showing more carbon dioxide under the hens than in incubators. 



The next point to determine was where the excess gas originated. 

 Both at Utah and at Guelph, the experiments seemed to indicate that the 

 excess supply came from the hen herself, though this point was not clearly 

 demonstrated. Apparently the hen was giving off carbon dioxide. Is this 

 the secret of the sitting hen? Is this the missing link? 



Following up this lead, we endeavored to show the effect of adding 

 carbon dioxide to the incubators. Varying amounts were added to different 

 machines, but this artificial supply seemed to injure the hatching. Here 

 was a little set-back. 



Pursuing this work along another line, the experiments at the Guelph 

 Station showed that the chicks hatched by hens contained more lime 

 than incubator chicks. They showed further that about the eleventh 

 day of incubation, (or when the embryo was eleven days old), there was 

 as much lime in the embryo as there was originally in the contents of the 

 egg, and at the end of the incubation period of twenty-one days the chicks 

 contained many times more lime than was originally in the egg contents. 

 Remembering the Utah tests which showed that carbon dioxide with 

 moisture decomposed the shell, is it possible that while weakening the shell 

 to allow the chick to make its escape, it at the same time liberates the 

 necessary lime for the body of the growing chick? This fact was deter- 

 mined by analysis of the chicks. 



Now a German experimenter has analyzed the shell at different stages 

 of incubation, and concludes that the shell is more than a simple protective 

 device. He says: "The egg shell doubtless shares in the exchange of 

 material of the egg contents during the incubation of the chick. The 

 material which disappears from the shell doubtless passes into the interior 

 of the egg. As to what way this "going in" (Absorption) takes place, and 

 what chemical changes render this possible; our investigations offer no 

 explanation. But he intimates the possibility of carbon dioxide abund- 

 antly produced in the egg, and penetrating through the shell playing an 

 important part here. 



These different experiments show: 



First That there is more carbon dioxide under sitting hens than in 

 incubators. 



Second That carbon dioxide with moisture decomposes the shell. 



Third That lime disappears from the shell during incubation. 



