MAINTENANCE AND WORKING REQUIREMENTS 49 



of 1,500 lbs. is got by multiplying by i|^, or I'S, or for 

 a horse of 600 lbs. by multiplying by ^^, or 0*71. 



In actual practice no such arbitrary standard can be 

 fixed to suit all cases and all animals. Every horse- 

 keeper knows that some horses will maintain their 

 condition, do their work satisfactorily, and, in short, 

 thrive, on less than the allowance found necessary for 

 the majority of the animals. Others will always require 

 an extra supply over the average allowance. These indi- 

 vidual cases have to be provided for, but the figures 

 given above are such as will be found practically useful 

 when applied to a number of animals, where the " good 

 doers " will practically balance the bad feeders. 



Whenever an animal is made to do work, the food 

 requirements are increased, and, as we have already 

 seen, all the nutrients in a foodstuff can take part in 

 supplying the energy needed. Energy exists in many 

 forms, and frequently energy in one form may be con- 

 verted into another. Thus the energy contained in a 

 ton of coal may be set free as light obtained from the 

 coal-gas, and this in its turn will give rise to heat, which 

 will in its turn produce steam sufficient to do mechanical 

 ivork. Now, there is a definite proportion between the 

 amount of light, and heat, and work got from this ton of 

 coal, so that, knowing the amount of heat generated, 

 the amount of work produced can be calculated. The 

 same holds good for the energy derived from food. 

 There is a definite ratio between the value of a food 

 as a heat-producer and as a work-producer. The relation 

 is such that the amount of heat required to raise the 

 temperature of 1 kilo. (2*2 lbs.) of water 1° C. is 



equivalent to 3,057 foot lbs., or ' foot tons, of work. 



Z,^40 



4 



