262 



VETERINARY PHYSIOLOGY 



production and heat production may be ascertained, as is 



Kgm. 

 212,500 



XT6^u • • • • • 



shown in the following table for a man : — 



Food 

 Work 



Calories. 

 3000 

 500 



2500 



6. Results of these Investigations. — Investigations by 

 these methods have shown that when there is an abundant 

 supply of carbohydrates and fats, they are used as the chief 

 source of energy, the carbohydrates being the more readily 

 used. 



Only when the work requires more energy than can be 

 supplied from these sources are the proteins used to any great 

 extent (fig. 13 6). But in a lean animal, i.e. an animal with no 



.WORV« 



Fig. 136. — To illustiate the influence of Muscular Work upon the Excretion 

 of Carbon dioxide and of Nitrogen — (1) in a fasting or underfed 

 animal; (2) in an animal fed on proteins; (3) in an animal on a 

 normal diet. 



great store of fats and carbohydrates, fed on proteins the 

 energy for work may be got almost entirely from them. 



All the three proximate principles of the food are 

 available, but the great use of proteins is in the growth and 

 repair of muscular tissue. 



It may therefore be concluded that, in a lean fasting animal 

 and in an animal fed on proteins, the muscles get their energy 

 chiefly from proteins, but that, in an animal with an adequate 

 store of fat or upon an ordinary diet, the muscles get it chiefly 

 from the carbohydrates of the food or from the fats of the food and 

 of the body. 



A study of the ordinary diet of horses doing muscular work 

 corroborates these conclusions. In this country the diet of 



