56 NUTRITION. 



it proceed from the decomposition of carbonic 

 acid gas. Thus the whole of this important 

 function, i. e. vegetable respiration, appears to 

 have for its object the fixing carbon in the 

 plant, while the result of animal respiration is 

 to diminish its quantity in the body, or in other 

 words, to supply animal heat by its combustion.* 

 It is well remarked by Mr. Hunt, that "The 

 animal kingdom is constantly producing car- 

 bonic acid, water in the state of vapour, nitro- 

 gen, and, in combination with hydrogen, ammo- 

 nia. The vegetable kingdom continually con- 

 sumes ammonia, nitrogen, water, and carbonic 

 acid. The one is constantly pouring into the 

 air what the other is as constantly drawing from 

 it, and thus is the equilibrium of the elements 

 maintained. 



" Plants may be regarded as compounds of 

 carbon, vapour, oxygen, hydrogen, and nitrogen 

 gases, consolidated by the all-powerful, all-per- 

 vading influences of the solar ray ; and all these 

 elements are the produce of the living animal, 

 the conditions of whose existence are also greatly 

 under the influence of those beams, which are 



* See Introduction to Practical Organic Chemistry, 

 p. 61. 



