48 SCIENTIFIC FEEDING OF ANIMALS 



(3) The energy metabolism. 



The simplest measure of the amount of energy 

 that can be obtained from any substance is the 

 heat which is produced when it undergoes com- 

 plete combustion. When, for instance, starch is 

 burnt in a bomb calorimeter filled with compressed 

 oxygen, a certain amount of heat is generated. 

 If the bomb is immersed in a known quantity of 

 water the rise in temperature of the water can 

 be measured by a very sensitive thermometer, and 

 from the observed increase of temperature of the 

 water, the amount of heat present in the starch 

 can be calculated. 



The unit of energy, expressed as heat, is the large 

 calorie (Cal.), which is the amount of heat sufficient 

 to raise i kilogram of water i C. (or i Ib. of water 

 4 F.). Sometimes the small calorie (Cal.) is em- 

 ployed, which is only a thousandth part of the 

 large calorie. When it is stated that the heat value 

 of i gram of starch (Ath of an oz.) is 4-1825 Cal., it 

 is understood that this is a direct measure of the 

 energy in the starch. In the same way, when it is 

 said that an ox weighing 600 kilograms (about 

 ii-J- cwt.) requires a daily supply of 12,780 Cal., it is 

 clear what is meant. It has already been seen that 

 many digestible components of the food yield 

 waste products which, like marsh gas and urea, 

 are combustible and so contain heat, or energy. 



