ENERGY IN FEEDINGSTUFFS AND ITS USES 93 



change it to kinetic form to warm the body, or to do work ; 

 or the animal can store a part of the potential energy of the 

 feed in the animal body in the potential form as fat. The 

 animal, however, is unable to utilize directly the kinetic 

 energy of the sun's rays as does the plant, and, consequently 

 the animal kingdom is dependent for its supply upon the 

 potential or stored-up energy of the vegetable kingdom. 

 Thus, besides furnishing the proteins and mineral matter 

 necessary for the repair and growth of the animal, the feed 

 is the sole source of the energy so essential to all the phe- 

 nomena of life. 



The units used for the measurement of energy are the 

 Calorie and the therm. A Calorie is the amount of energy 

 in the form of heat required to raise the temperature of 

 one kilogram of water through one degree Centigrade, or 

 of one pound of water through four degrees Fahrenheit. A 

 therm is one thousand Calories. When speaking of the 

 energy values of feedingstuffs, the therm is used more gen- 

 erally ; while when speaking of the energy values of human 

 foods, the Calorie is commonly used. 



Gross Energy or Heat of Combustion. — The total amount 

 of energy stored in a feedingstuff is called its gross energy 

 or the heat of combustion. The gross energy of a feed 

 is determined by burning it in an apparatus known as the 

 homb calorimeter, which consists essentially of a steel cyl- 

 inder or bomb surrounded by a known quantity of water. 

 A sample of the feedingstuff is placed in the bomb, which is 

 then filled with oxygen to insure complete combustion. The 

 sample is ignited by means of an electric current, and the 

 amount of heat liberated in the combustion is determined 

 from the rise in the temperature of the water surrounding 



