902 The Feeding oe Farm Stock. [fee., 



of the different nutrients present in digestible form in average 

 samples of the commoner feeding-stuffs, together with other 

 information, the use of which will be explained subsequently. 



The varied functions that the digested nutrients are re- 

 quired to sustain in the animal may be summarised briefly 

 as follows : — 



(a) Supply of Heat. 



The temperature of the body must not fluctuate to more 

 than a very slight extent if normal health is to be main- 

 tained. The losses of heat from the body — for the body 

 is almost continually warmer than the surrounding atmo- 

 sphere, and hence radiates heat — must therefore be made 

 good by the production of heat in the body from the food. 



(b) Supply of Mechanical Energy. 



Even in the case of an animal completely at rest, a 

 certain amount of mechanical energy is needed for the 

 performance of the indispensable internal work of the 

 body (e.g., for maintaining the movements of the heart, 

 lungs, &c), and for the labour involved in the mastication 

 and transmission of the food through the digestive 

 system. The performance of this work demands a supply 

 of energy just as surely as the movements of a steam- 

 engine are dependent upon a steady supply of mechanical 

 energy in the form of expanding steam. 



(c) Supply of materials to make good the normal wear and 



tear of the vital processes. 



In other words, the live-weight of the animal must be 

 maintained. All vital activity involves the destruction 

 of various ingredients of the body, and it is obvious, 

 therefore, that unless the materials so lost be replaced 

 the animal must lose flesh rapidly and will sooner or 

 later die of exhaustion. This replacement can only be 

 effected by materials digested from the food-supply. 

 All the foregoing requirements are fundamental, and hold 

 good for all classes of animals. In many cases, however, there 

 are still further requirements that the food must meet, viz. : — 



(d) Supply of material necessary for the support of any pro- 

 ductive activity of the animal. 



In all cases where the animal is either producing new 

 substance (e.g., growth, in the case of young animals; 

 fattening increase, milk, wool, &c), or is expending mus- 



