CHAP. v. FUNCTIONS OF FOOD. 981 



CHAPTER V. 



ON THE QUALITIES AND COMPARATIVE VALUES OF FOODS FOR LIVE 



STOCK. 



FOOD is the raw material from which animals build up and maintain 

 their bodies. Even an adult animal not increasing in weight and 

 doing no work, such as a " store " ox or " store " sheep, 1 consumes a 

 certain daily allowance of food, without which it would rapidly become 

 thin and die in other words would starve. Food given in a propor- 

 tion over and above that required for the mere maintenance of life and 

 normal weight either goes to aid growth (in young animals), or to pro- 

 duce that increase in weight called " fattening " (in mature stock), or 

 it is spent in producing work (as in horses and draught oxen). Food 

 given in excess beyond the maximum which the animal can utilise for 

 these purposes is simply undigested or (qua food) is wasted. 



One of the chief facts that occur to &ny one thinking for the first 

 time about the properties of the animal body, as distinguished from 

 vegetable organisms, is that animals have a high temperature. Animal 

 life is at once associated in our minds with warmth, and coldness with 

 death. That heat cannot be produced, or kept up, in an ordinary fire 

 without the continual consumption of material (fuel) is familiar to us 

 all, the heat of the fire being the result of the chemical process of 

 combustion, which is merely rapid oxidation, that is to say rapid 

 chemical combination between the wood or coal used as fuel and the 

 oxygen which is the main active constituent of the air. The heat of 

 the animal body is produced very similarly by a process of combus- 

 tion in which the air taken into the animal's lungs serves to combine 

 through the medium of the blood with the products of digested food, 

 burning them up and producing heat. The process is less rapid and 

 less fierce than when coal is burnt in a fire, but ultimately the result is 

 much the same, and in order to keep up this burning or oxidation pro- 

 cess in the blood of the animal we must supply it with its necessary 

 " fuel " i.e. food. The animal body, like all other warm things, rapidly 

 radiates or gives off its heat to the surrounding air, so that, in order 

 to maintain its temperature the production of heat must be always 

 going on. If the supply of fuel (food) is neglected, Nature still keeps 

 up the heat for a while at the expense of certain reserve fuel (mainly 

 fat) which the animal has stored up in its tissues, and when this 

 becomes exhausted, even the muscular tissues themselves are gradually 

 used up the animal getting thinner and thinner (starving) until a 

 point is reached at Avhich the substance of the body has been so far 

 used up that the various organs refuse to carry on their vital functions, 

 and then the animal dies of starvation. 



The combustion of food serves other purposes besides the mainten- 



1 A " store " animal is defined as one not yet put upon fattening food. 



