68 



» 



work is still further increased the respired air amounts to 450 to 500 

 liters (475 to 528 quarts) per minute — in other words, 14 to 15 times what 

 it was when no work was performed. However, in these different 

 cases the ratio of carbon dioxid to oxygen has been found to var}- 

 very little. 



PROPORTION OF ENERGY OF FOOD EXPENDED FOR INTERNAL 

 AND EXTERNAL MUSCULAR WORK. 



A horse converts 38.3 per cent of the energy of food into mechanical 

 work. On account of the energy' required for respiration, the beating 

 of the heart, etc. , only about 34 per cent of the energ}' of the food is 

 actually available for external muscular work. The best record for a 

 steam engine is said to be an efficieney per indicated horsepower of 

 22. T per cent on the basis of total heat supph'. Per delivered horse- 

 power the amount is probably 10 per cent less. The animal is there- 

 fore seen to be a much more efficient machine than the engine. 



Tests were made with a horse walking on a level, walking up an 

 incline, and hauling a load on a level, and it was fovmd that in the last 

 case the energy of the food was not quite so economically used as in 

 the first case. On the basis of his experiments, Zuntz computes that a 

 horse weighing 500 kilograms (1,100 pounds) and performing no work 

 requires 3,201 grams (7.1 pounds) of total nutrients containing 1,382 

 grams (3 pounds) of crude fiber. By total nutrients is meant the sum 

 of the protein, carbohydrates, and fat multiplied by 2.4.^' Of this quan- 

 tity of total luitrients not less than 2,100 grams (4.6 pounds) is required 

 for the internal muscular work expended in digesting- and assimilating 

 the food, and 1,1(»0 grams (2.4 pounds) for other purposes (largely 

 some form of internal nniscular work). Zuntz found that the amount 

 of food required was affected by anything that disturbed the horse. 

 In one experiment a horse confined in a stable was much disturbed by 

 flies and consequently restless. The increased work in fighting the 

 files caused an increase of 10 per cent of the carbon dioxid excreted. 

 This means that more food material was burned in the body than was 

 the case when the horse was quiet, for the combustion of food in the 

 body, it will be remembered, furnishes the carbon dioxid excreted in 

 the breath. 



In addition to other matters, Zuntz noted that the effect of body 

 conformation had a marked effect on the economical production of 

 work. He found that defects in external conformation and move- 

 ments necessitate an increased amount of muscular exertion. This 

 has an miportant bearing upon the market value of the horses. Too 



«Ziintz uses this factor instead of 2.25, the factor commonly used by American 

 investigators. 



