914 NUTRITION AND HEAT REGULATION. 



system or by hypersecretion of the adrenal glands or the hypophy- 

 sis, in which case hyperglycemia and glycosuria result. Or the 

 glycogenetic tissues may be inadequate to handle all the sugar 

 absorbed from the alimentary canal (alimentary glycosuria). 

 and in this case also there is a temporary hyperglycemia and 

 glycosuria. At the consumption end the amount of sugar de- 

 stroyed is controlled by the energy needs of the tissues, especially 

 of the muscles. Failure to destroy the sugar at this point brings 

 on also a hyperglycemia and glycosuria of a more serious nature. 

 Our sugar-regulating mechanism in fact may prove inadequate 

 in one of four general ways, which may be tabulated briefly as 

 follows : 



1. Conversion of sugar to glycogen (liver) breaks down in 

 alimentary glycosuria. 



2. Conversion of glycogen to sugar (liver) breaks dovm in 

 injuries to the central nervous system, excessive internal secretion 

 by adrenal gland, etc. 



3. Glycolysis of sugar (muscles and other tissues) breaks down 

 in diabetes mellitus and pancreatic diabetes. 



4. The normal impermeability of the kidney breaks down in 

 phlorhizin diabetes. 



Functions of the Carbohydrate Food. — The general value of 

 the carbohydrate food to the organism ma}^ be summarized as 

 follows: (1) It furnishes a source of energy for the needs of the 

 tissue cells and particularly for muscular work. It will be remem- 

 bered that the glycogen of a muscle disappears in proportion 

 to the work done by the muscle, and, indeed, prolonged muscu- 

 lar work, especially during starvation, may wipe out quickl}- the 

 entire store of glycogen in the body, in the liver as well as in 

 the muscles. It is usually believed, thereicre. that the oxida- 

 tion of the sugar furnishes energy which eventually by the machin- 

 ery of the muscles is utilized to do work. 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 important 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 sontraction takes 

 the form of heat, and even during 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 



