CARBOHYDRATES AND FATS. 825 



series of oxidations may occur such as is represented in the following 

 formulas: 



CH 2 OH COOH COOH COOH 



(CHOH) 4 (CHOH) 4 (CHOH) 4 COOH 



COH COH COOH 



Dextrose. Glycuronic acid. Saccharic acid. Oxalic acid. 



We are certain at present only of the fact that the final products 

 are carbon dioxid and water that is, complete oxidation products 

 and that in some way the internal secretion of the pancreas is 

 essential to the process. 



Functions of the Carbohydrate Food. The general value of 

 the carbohydrate food to the organism may be considered under 

 three heads: (1) It furnishes a source of energy for muscular 

 work. It will be remembered that the glycogen of a muscle dis- 

 appears in proportion to the work done by the muscle, and indeed 

 prolonged muscular work, especially during starvation, may wipe 

 out quickly the entire store of glycogen in the body, in the liver as 

 well as in the muscles. It is usually believed, therefore, that the 

 oxidation of the sugar furnishes energy which by the machinery 

 of the muscles is utilized to do work, that is, to cause muscular 

 contractions. It seems probable that under normal conditions this 

 material furnishes the main, if not the sole source of energy for 

 muscular work. (2) The oxidation of the sugar furnishes an im- 

 portant part of the constant supply of heat needed by the body. 

 Each gram of sugar on oxidation yields 4 Calories of heat, and, 

 since the carbohydrates form the largest part of our diet and are 

 easily oxidized in the body, they must be regarded as an especially 

 available material for keeping up the supply of animal heat. The 

 largest part of the energy liberated by the oxidation of sugar in the 

 muscles during contraction takes the form of heat, and even dur- 

 ing muscular rest the condition of tone is probably attended by a 

 constant oxidation of this material. (3) The oxidation of the sugar 

 protects the protein of the body. Attention has already been 

 called to the fact that an animal may be kept in nitrogen equilibrium 

 on a relatively small protein diet provided carbohydrates (or fats) 

 are also eaten. One may say, in fact, that as the carbohydrate food 

 is increased the protein food may be diminished, down to a certain 

 irreducible minimum. From the chemical composition of carbo- 

 hydrates it is evident that they alone cannot serve to build up 

 protoplasm. An animal fed on carbohydrate food alone, no 

 matter how abundant the supply, would eventually starve to death. 

 Within certain limits, however, the carbohydrates are protein 

 sparers; the energy provided by their oxidation keeps up the supply 

 of heat and enables the muscles and probably the other tissues to 

 function normally, and to this extent protects the living protein 



