DYNAMICS 157 



Application of the Principles. The energy expended in 

 the work of digestion differs only in respect of the fact that 

 when the animal does external work it consumes more food, 

 and the work of digestion is correspondingly increased. But 

 as the heat derived from this additional internal work also 

 helps to maintain the temperature of the body, an equivalent 

 amount may be deducted from the maintenance ration. 



For example, suppose it has been found that a certain 

 horse requires a food equivalent to 35 kt. per day for main- 

 tenance, and that the static value of the hay is 1*83 kt. per 

 lb., then [35 -f- 1-83 ] 19'! Ibs. is the quantity of hay required. 

 Further, if the animal, on being put to work, does 9*6 million 

 foot-pounds per day, since 463,200 foot-pounds can be 

 obtained from T kt. of dynamic energy, [9*6 -f- 0-4632 =] 

 20*7 kt. is required for the whole. If the additional food 

 required for the work be given in the form of oats, the dynamic 

 value of which is 2*5 kt. per lb., then [207 -"- 2*5 =] 8*3 Ibs. 

 is the quantity required. But the thermic value of tKe oats 

 is 2 '6 1 kt. per lb., and 8'3 Ibs. would, therefore, furnish 

 [V6i X 8*3 =] 21*7 kt. The difference between these two 

 numbers [217 207 =] i kt. represents the energy expended 

 on the work of digesting the oats ; and, as this energy appears 

 as heat in the body of the animal and helps to maintain its 

 temperature, a quantity of hay (0*54 lb.) equivalent to i kt. 

 (thermic) may be withdrawn. 



It will be seen, therefore, that the ration for simple main- 

 tenance is 19*1 Ibs. of hay, but the ration for work is 18*56 Ibs. 

 of hay and 8-3 Ibs. of oats. The amount of hay (0-54 lb.) which 

 can be withdrawn is so small that it can be ignored. And 

 this is usually the case, because the concentrated foods given 

 for working rations are usually very easily digestible, and 

 very little energy is expended on the process. 



If a large amount of fodder of a coarser character were 

 added to the original maintenance ration the case would be 

 different. Suppose, for example, that it were possible to 

 derive the stipulated amount of work from hay, the quantity 

 required would be 9-6 -=- (0*4632 X n) = i8'8 Ibs. But this 

 amount is not to be added to the original maintenance ration ; 



