146 THE CHEMISTRY OF CATTLE FEEDING 



injurious to the health of the animals. As regards the latter 

 point his apprehensions have proved to be unfounded ; and 

 though he adduced weighty experimental evidence in favour 

 of the former, his views have not prevailed. Almost every 

 recognised authority now recommends that the amount of 

 protein in the maintenance ration should be increased when 

 the animal is put to work. 



Work. The amount of additional food should be pro- 

 portional to the work done. In order to investigate this 

 question, it is necessary to select some standard for the 

 measurement of work. The force of gravity is universally 

 adopted for this purpose, and work is measured in terms of 

 the resistance overcome. The amount of this resistance at 

 any one place is proportional to the mass of the substance 

 raised ; and, for the present, the variation from place to place 

 may be disregarded. 



In English standards the unit of work is a foot-pound, i.e. 

 a mass of one pound raised one foot high. Obviously, 

 double the amount of work (2 units) is done when two 

 such masses are raised one foot, or when a mass of one 

 pound is raised two feet high. In short, the mass (in pounds) 

 multiplied by the height (in feet) through which it is raised 

 gives the number of units of work done. All work, whatever 

 the nature of the resistance overcome, is measured in the 

 same units (foot-pounds). 



The energy expended in doing work is not anihilated, 

 but merely transformed. It all appears ultimately in the 

 form of heat. Some of the energy may be converted tem- 

 porarily into the potential form ; but when it is reconverted 

 into the kinetic form, this also appears as heat. A very 

 definite relationship between work and energy has thus been 

 established. It was shown by Joule that when all the 

 potential energy represented by 772 foot-pounds of work 

 is converted into the kinetic form of heat, it will raise 

 the temperature of one pound of water iF. That is what 

 is meant when it is said that 772 foot-pounds of work is 

 the mechanical equivalent of heat. 



On the Centigrade scale, the degrees are r8 times larger 



