CONSUMED IN RESPIRATION. 67 



form of carbonic acid and water, and their conversion 

 into oxidized products furnishes the clearest proof, that 

 far more oxygen is absorbed than is required to convert 

 the carbon and hydrogen of the metamorphosed tissues 

 into carbonic acid and water. 



The change and metamorphosis of organized tissues 

 going on in the vital process in the young animal, con- 

 sequently yield, in a given time, much less carbon and 

 hydrogen in the form adapted for the respiratory process 

 than corresponds to the oxygen taken up in the lungs. 

 The substance of its organized parts would undergo a 

 more rapid consumption, 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 development of the organs in the 

 young animal, are dependent on the presence of foreign 

 substances, which, in the nutritive process, 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 con- 

 sumed ; that is, growth, or increase of mass in the 

 body, the consumption of oxygen 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 substances devoid 

 of nitrogen, which their organism cannot employ for 

 nutrition, strictly so called, that is, for the production 



