RESPIRATION. 291 



monest operations of the great Creator in the 

 world around ! 



As yet that is, previous to the eighteenth day 

 of incubation, the chick does not use its lungs. It 

 is unable to breathe. Yet it is well known to most 

 persons that respiration is absolutely necessary to 

 life in every condition, whether in its infancy or in 

 its maturity. By the term respiration it is proper to 

 understand, that change in the blood which is pro- 

 duced by its exposure to air and not merely the 

 act of inspiring and expelling a quantity of air 

 from the lungs. Fish and aquatic insects respire, 

 although they do not breathe the air we breathe ; 

 but in their cases the blood is exposed to air dis- 

 solved in the water in which they swim. It is to 

 be inquired, therefore, whether respiration goes on 

 in the chick during the first eighteen days of its 

 existence within the shell. If we open the shell 

 about the twelfth day, it has been described as 

 exhibiting one of the most splendid spectacles that 

 occurs in the whole organic creation. A multi- 

 tude of blood-vessels are seen ramifying upon 

 the surface of the membrane enveloping the 

 chick, which convey blood to and from its body. 

 It is generally considered by physiologists, that 



