CONSUMED IN RESPIRATION. 69 



animal, consequently yield, in a given time, much 

 less carbon and hydrogen in the form adai)ted for 

 the resj^iratory process than corresponds to the 

 oxygen taken up in the lungs. The substance of 

 its organised parts would undergo a more rapid con- 

 sumption, and would necessarily yield to the action 

 of the oxygen, were not the deficiency of carbon 

 and hydrogen supplied from another source. 



The continued increase of mass, or growth, and 

 the free and unimpeded developement of the organs 

 in the young animal, are dependent on the presence 

 of foreign substances, which, in the nutritive pro- 

 cess, have no other function than to protect the 

 newly-formed organs from the action of the oxygen. 

 It is the elements of these substances which unite 

 with the oxygen ; the organs themselves could not 

 do so without being consumed; that is, growth, or in- 

 crease of mass in the body, the consumption of oxy- 

 gen remaining the same, would be utterly impossible. 



The preceding considerations leave no doubt as 

 to the purpose for which Nature has added to the 

 food of the young of carnivorous mammalia sub- 

 stances devoid of nitrogen, which their organism 

 cannot employ for nutrition, strictly so called, that 

 is, for the production of blood ; substances which 

 may be entirely dispensed with in their nourishment 

 in the adult state. In the young of carnivorous 

 birds, the want of all motion is an obvious cause of 

 diminished waste in the organised parts ; hence, 

 milk is not provided for them. 



