DEVELOPMENT OF PARTS. 283 



sight to watch the heart now beating, and propel- 

 ling the clear red blood through the numerous 

 translucent tubes which ramify over the surface of 

 the yolk. 



By exposing the egg at this period to the in- 

 fluence of cold, it will be seen that the beating of 

 the heart ceases. It first becomes gradually slack- 

 ened, until finally it ceases to beat altogether. But 

 the life of the little being is not now necessarily de- 

 stroyed, unless the cold applied is too severe. The 

 whole of the phenomena may be reproduced, by 

 simply putting the egg into warm water. In pro- 

 portion as the heat rises, the little heart begins to act 

 again, until when it has reached its former degree, 

 its pulsations are as frequent as they were before. 

 If the heat is raised to 115 or 120, the heart will 

 be seen to beat much quicker than before. On 

 again applying cold the movements diminish in 

 frequency, until they cease entirely. As may 

 readily be imagined, the application of any corro- 

 sive acid, or poisonous chemical ingredient, soon 

 puts a stop to the whole phenomena of life in the 

 chick ; and in this instance they cannot be renewed. 

 These facts are important, since they show us 

 that the temporary absence of the parent bird 



