194 ORGANIC AGRICULTURAL CHEMISTRY 



dicated, for lactic acid, which is a normal constituent of muscles, 

 is probably an intermediate product. 



The rate at which this oxidation takes place is dependent 

 upon the activity of the muscle cells. Certain muscular activi- 

 ties, such as the involuntary actions of the body connected 

 with the maintenance of body heat, body tone or tension, and 

 the processes of circulation, respiration and digestion, are con- 

 stantly going on and a large part of the energy of the food of 

 animals is so expended. Another part of energy of animal food 

 is used for producing muscular work which is voluntary, and 

 varies with the physical or muscular activity of the animal. 

 The total energy demands of the body regulate the demands 

 upon the supply of glucose in the blood, and thus upon the 

 reserve supply of glycogen in the liver. In general it may be 

 said that under normal conditions of feeding and activity the 

 supply of glycogen in the liver is used up between two succeed- 

 ing meals. 



Muscle Glycogen. — The liver is not, however, the only place 

 where carbohydrate food is stored in reserve in the form of 

 glycogen. In case the maximum amount of glycogen has been 

 stored in the hver and the supply of carbohydrate food is still 

 in excess of the energy demands of the body, then the glucose 

 of the general circulation on reaching the muscle cells is not all 

 oxidized but, here likewise, is partly converted into glycogen 

 and stored in the muscles as muscle glycogen. The amount 

 possible of storage in this form may attain a maximum of 2.0 

 per cent of the muscles which, though less in percentage amount 

 than in the liver, may amount in total to much more, owing to 

 the far greater mass of the muscle tissue over that of the liver. 

 With an increase in the energy demands of the body or a de- 

 crease in the food supply, this muscle glycogen is first drawn 

 upon, being converted back into the form of glucose: In all of 

 these metabohc changes enzymes play a most important part. 

 Probably each metabolic reaction is brought about through 

 their agency. 



