186 THE CHEMISTRY OF THE FARM 



of the load which he has to move, the distance he has 

 to travel, the inclination of the road, and the time 

 given for the accomplishment of the task. From 

 these data the quantity of available food needed for 

 the production of the required work can be calculated. 

 To this amount must be added an amount of available 

 food sufficient for the internal work of the body (diges- 

 tion labour excepted) when the animal is at rest. This 

 amount we have already seen (p. 182) is about 2*4 lbs. 

 (one-third of 7 lbs.) for a horse of 1,100 lbs. live weight. 

 We thus arrive at the total quantity of available food 

 required for muscular exertion. The ration must 

 besides this include an amount of digestible matter 

 sufficient to provide for the labour of digestion : this 

 is not a fixed quantity, but will vary according to the 

 description of food used, and will be greatest when 

 straw chaff is employed. The total amount of food 

 must, of course, produce sufficient heat to maintain the 

 temperature of the body. 



One of Zuntz's examples is that of a horse plough- 

 ing eight hours a day. The horse with harness is 

 assumed to weigh 1,144 lbs. ; he walks at the rate of 

 2^ miles per hour, drawing a plough the draft of 

 which is 147*4 lbs. The total work accomplished is 

 8;967 foot-tons, requiring 11'63 lbs. of available food. 

 Adding 2*4 lbs. for other work (excluding digestion), 

 we have a total requirement of 14*03 lbs. of available 

 food for the day's ration during this heavy work. 

 The table on p. 184 shows that this amount of avail- 

 able food would be supplied by 20 lbs. of maize, 

 which would at the same time supply enough energy 

 for its own digestion. A diet of maize only is, of 

 course, impracticable; but the same table shows 



