The Animal Body. 217 



easily oxidized than sugars and require a larger intake of oxygen 

 for their combustion; but when oxidized they yield more heat 

 per pound than any other food ingredient. 



The carbohydrates of the food are chiefly starch, sugars, cel- 

 luloses and pentosans. Various other non-nitrogenous constit- 

 uents of food, such as the pectins, lignin and vegetable acids, 

 are generally included under this title, though they are not, 

 strictly speaking, carbohydrates. Carbohydrates form the larg- 

 est part of all vegetable food. They are not permanently stored 

 in the animal body, but serve when burned in the system, for 

 the production of heat and mechanical work. If a fattening 

 steer were consuming 16 pounds of digestible organic matter and 

 gaining two pounds of live weight daily, the body increase and 

 urine would contain not over 2.5 pounds of dry matter, leaving 

 not less than 13.5 pounds to be oxidized, of which 12 pounds 

 might consist of carbohydrates and fat, mostly the former. 



The carbohydrates are also capable, when consumed in excess 

 of immediate requirements, of conversion into fat. The well- 

 recognized value of corn meal as a fattening food, a feeding stuff 

 nearly seven-tenths of which consists of starch and similar struc- 

 tures, is a practical illustration of this truth. 



The carbohydrates and fats are the natural fuel food stuffs of 

 the body. They cannot serve for the renewal or upbuilding of 

 tissue, but by oxidation they constitute an economical fuel for 

 maintaining body temperature and for power to run the bodily 

 machinery. Proteins may likewise serve as fuel, but this is ap- 

 parently confined to a non-nitrogenous part of their molecule. 

 When fats or carbohydrates are available the proteins of the tis- 

 sue are not normally consumed for production of heat and force. 

 Only when the former are lacking will the animal increase its 

 protein metabolism and nitrogen output for purposes of main- 

 taining the body temperature. A moderate quantity of protein 

 supplied to a growing animal will thus produce a much larger 

 increase of muscle when accompanied by a liberal supply of car- 

 bohydrates or fats. In this case, the non-nitrogenous constit- 



