CHAPTER IX 



THE COMPOSITION OF PLANTS AND 



ANIMALS 



In our study of the organic compounds which are of im- 

 portance in connection with plants and animals from the agri- 

 cultural standpoint we gave especial attention to three groups, 

 viz. carbohydrates, fats and proteins. These three groups com- 

 prise all of the essential organic food materials of both plants and 

 animals. Only relatively few compounds outside of these three 

 groups were mentioned, for example, lactic, malic and tartaric 

 acids, some of the esters in addition to the glycerol esters or 

 fats, urea, uric acid and some others. The last two we shall 

 find are physiologically directly connected with the proteins. 

 The others, and some which were not mentioned at all, while 

 they are no doubt essential to the life history and environment 

 of the plant or animal, are nevertheless not essential in the same 

 way as the carbohydrates, fats and proteins, i.e. as food ma- 

 terials. As the relationship of plants and animals to their food 

 supply is the primary one in their agricultural connection we 

 see that in a study of agricultural chemistry these three groups 

 of compounds occupy a predominant position. 



Organic and Inorganic Constituents. — In their chemical 

 composition plants and animals may be readily shown to con- 

 sist of two distinctly different kinds of material, viz. organic 

 and inorganic. Considering the definition of organic com- 

 pounds which we derived from our study of organic chemistry, 

 we term organic any compound which in its constitution is 

 proven to be derived from the fundamental compounds of carbon 

 and hydrogen, the hydrocarbons. As such, the organic com- 

 pounds present in plants and animals contain, in most cases, 



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