CHAPTER XI 



ANIMAL FOOD AND NUTRITION 

 DIGESTION AND ABSORPTION 



ANIMAL FOOD 



We have now to consider the question as to how and in 

 what form the food reaches the cell and how the fundamental 

 oxidation reaction is brought about. It is impossible to in- 

 vestigate these processes with the single cell, but as the animal 

 organism as a whole utilizes its food for the production of energy 

 just as the single cell does, we are able to understand the chemical 

 reactions by which food is eventually converted into energy by 

 making a study of the way in which it is accomplished in the 

 animal body. Furthermore, it is not possible to study these 

 processes in the plant with the same detail that we can in the 

 animal for the simple reason that they have not yet been worked 

 out in the plant, because in the plant they are masked or over- 

 shadowed by the predominating constructive processes. We 

 shall, therefore, turn our attention from the single cell as such, 

 which is alike in its fundamental chemical processes in both 

 plants and animals, to the consideration and study of the animal 

 as a whole and the chemical processes by which it utilizes its 

 food material primarily for the liberation of energy. 



Definition of Food. — As we have previously stated in a 

 general way, the chemical composition of the animal body 

 while it is made up of very complex individual compounds is, 

 nevertheless, simple in that they are all comprised in the three 

 groups, carbohydrates, fats and proteins, together with some 

 inorganic salts. These latter are found mostly in the skeleton 

 part of vertebrate animals and in small amounts in the various 

 animal fluids, where they perform important functions, but in 



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