156 NUTRITION OF FARM ANIMALS 



organs, constituting the adipose tissue (94). This tissue con- 

 stitutes a reserve of non-nitrogenous material which may be 

 mobilized later if need arises. 



Of the chemistry of the conversion of carbohydrates into 

 fats, as well as of the organ or organs where it is effected, 

 our knowledge is still meager, but the fact of such a change 

 is undisputed and it is perhaps the most notable example 

 of a synthetic and anabolic process in the animal body. 

 The physiological evidence for this fact and the quantitative 

 relations of the process may be taken up more conveniently 

 later (249). 



218. Katabolism of carbohydrates. The physiological sig- 

 nificance of the dextrose of the blood and the glycogen of the 

 muscles and liver appears most clearly when they are regarded, 

 not in the light of a more or less temporary storage of matter 

 in the body, but rather as carriers of energy for the physiological 

 processes. Of these processes, the most obvious one, which 

 vastly predominates over all others, is the performance of work 

 by the muscles, external and internal, but what is true of mus- 

 cular work is in the main true also of the subordinate forms of 

 glandular and cellular activity. The former, therefore, may 

 be taken as typical. 



In the performance of muscular work, as will appear later, 

 there is a rapid katabolism of non-nitrogenous material and 

 especially of carbohydrates, largely, it would appear, in the form 

 of dextrose. The resulting impoverishment of the blood in 

 dextrose causes a conversion of stored up glycogen into dextrose 

 to supply the lack. If the view of the formation of glycogen 

 which regards it as a reversible reaction may be accepted, we 

 may say that the chemical equilibrium between the dextrose 

 and the glycogen is disturbed by the removal of the former 

 during muscular work. As long as the work is continued, the 

 process of conversion of glycogen into dextrose also continues, 

 and by prolonged work it is possible to reduce the glycogen con- 

 tent of an animal to a very low limit. 



It should be clearly understood that the foregoing is only a 

 highly schematic view of the chemistry of muscular contraction 

 as related to the katabolism of the carbohydrates. Some further 

 consideration is given in Chapter XIV (630) to the very com- 

 plicated chemical mechanism of the process. 



