l6o ORGANIC AGRICULTURAL CHEMISTRY 



which functions they bear no direct relation to the energy of 

 the living animal. Different animals and different organs of 

 the same animal contain different individual compounds of the 

 three groups, but, considered as a whole, and in general, the 

 living cellular portions of the animal body are composed of 

 carbohydrates, fats and proteins. It will thus be natural to 

 find that the organic or energy food of animals consists of these 

 three groups of compounds, for out of these food materials the 

 body substance of the animal must be formed and from them 

 the energy of the ^nimal is derived. 

 r Animal food has b^en defined as " anything, which taken into 

 the animal body is utilized by the animal for the building up of 

 body substance or for the production of energy." 



Utilization of Food. — In order that the miscellaneous food 

 may thus be utilized to build cellular material or to furnish 

 energy by oxidation, it is necessary for it to undergo certain 

 changes. In other words, the food material must fit the condi- 

 tions of the animal body. The changes which the food thus 

 undergoes are included in the various processes known by the 

 general name of digestion. 



After the food has been put in the proper condition by the 

 processes of digestion, it must then be taken up by the circulating 

 fluid of the body and conveyed to the cells and organs where 

 later changes occur. This process is known as absorption. 

 The digested and absorbed food then undergoes other changes 

 necessary for conversion into body substance or for oxidation. 

 These changes are included in the processes known as metabolism. 

 The final change in metabolism is always oxidation with the 

 liberation of energy and the formation of certain waste prod- 

 ucts. These waste products are then eliminated from the body 

 by the processes of excretion. 



Thus the food is subjected to the two main processes of 

 digestion and metabolism, with the secondary processes of 

 absorption and excretion. For the purpose of considering the 

 food of animals we may, therefore, divide the animal body into 

 four regions, viz. (a) the region of digestion, where the food is 



