78 



FEEDS AND FEEDING, ABRIDGED 



thru the oxidation of these two carbohydrates. Tho the supply in the 

 body tissues at any one time is small, glucose is continuously being 

 formed from the food nutrients or body tissues, to replace that used 

 up during work. 



The animal as a machine. — Numerous experiments have shown that 

 animals at moderate work can convert into external work from 29 to 

 37 per ct. of the total energy expended. On the average, about one- 



Fig. 23. — The Muscular System of the Horse 



The work done yearly in this country by horses and mules is worth over $2,- 

 000,000,000. (From Ellenberger. ) 



third of the energy used by men or animals in muscular exertion is 

 recovered as useful work. The rest takes the form of heat within the 

 body, and is lost so far as the production of work is concerned. These 

 figures do not take into account the energy lost in the excreta, that 

 expended for digestion and assimilation, or that used in maintaining 

 the body when at rest. Allowing for all of these, a man actually con- 

 verts about 20 per ct. of the fuel of his food into external work. The 

 best steam engines have about the same efficiency, while the average 



