METABOLISM 191 



as anabolism, and the tearing-down and oxidation process as 

 kataholism. The double process is termed metabolism. 



MetaboUsm then means the double process by which the 

 digested and absorbed animal food is first built up by anabolism 

 and then torn down by katabolism, in which latter process energy 

 is liberated, thus fulfilling the complete function of food. The 

 entire double process includes all the changes which the original 

 food material undergoes subsequent to digestion and absorption. 

 These latter processes simply prepare the food and convey it 

 to the animal cells where the metabolic changes take place. 



As will be readily understood, this process of metabolism is 

 not simple, but becomes often very complicated both because of 

 partial changes and because of transformations from one form 

 of substance into another. Many of the intricate changes 

 occurring in metabolism have not yet been made clear by 

 means of physiological and physiological-chemical investiga- 

 tions, but are still subjects of discussion and experimentation. 

 It will not be profitable, therefore, in this study to enter into 

 the discussion of many of these questions. We shall consider, 

 therefore, only the fundamental facts and certain details which 

 have been well established by experimental evidence. 



METABOLISM OF CARBOHYDRATES 



Direct Metabolism 



The metabolic changes which carbohydrate food undergoes 

 in the animal body are more thoroughly understood than are 

 those of either fats or proteins. We shall discuss these changes 

 more fully than those of the other two food constituents, not 

 because they are more important, but because they can be 

 made clearer in an elementary treatment. 



As previously explained, the carbohydrate food which is 

 eaten by an animal is changed by the combined digestive actions 

 into the form of the three common hexose monosaccharoses, 

 viz. glucose, fructose and galactose. In the normal diet of a 

 mature animal, in which starch is the predominating carbo- 



