DYNAMICS 145 



oxgyen are absorbed, and more carbon dioxide and water are 

 given off. It is impossible, therefore, to resist the conclusion 

 that the energy for the performance of animal work is derived 

 mainly, if not entirely, from the oxidation of the non-nitro- 

 genous matter. 



It is clear, then, that when animals do work, the available 

 energy of the rations must be increased by additions of 

 digestible fat and carbohydrates. There is no dissent from 

 this proposition. It is unanimously agreed to by theorists and 

 by practical men alike. 



It has also been inferred that it is unnecessary to increase 

 the amount of nitrogenous matter of the food beyond what is 

 required for the maintenance of the animal when at rest. It 

 must be recognised, however, that all animals, when put to 

 hard work, exhibit a strong desire for more nitrogenous foods. 

 We should not perhaps be justified in regarding their desires 

 as an indication of their requirements, but it is found that 

 such food markedly increases their capacity for work. 



It will be shown presently that the amount of additional 

 food required for work is large. In some cases it is greater 

 than the quantity required for the maintenance of the animal 

 when at rest. When large amounts of carbohydrates are 

 added to or included in the ration, the amount of nitrogenous 

 matter must be correspondingly increased (p. 106) to enable 

 the animal to digest it properly. 



The excess of protein, beyond what is required for the 

 maintenance of the animal, is rapidly resolved into amino- 

 compounds ; and it is known that these substances when directly 

 ingested have a powerful stimulating effect. The animal is 

 thus induced to put forth greater effort and so to utilise the 

 potential energy of the additional food. 



It is doubtful whether these considerations can be regarded 

 as affording an adequate explanation of the beneficial effects 

 of increasing the amount of protein as well as of the fat and 

 carbohydrates in the food of animals when they do work. 

 Probably something more remains to be discovered. Chitten- 

 den indeed has questioned the fact. He maintained that excess 

 of protein was not only unnecessary, but might even prove 



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