4 THE CHEMISTRY OF CATTLE FEEDING 



of the food. The circulation of the blood is a form of work 

 which may be compared to pumping water from a well. The 

 operation of the processes of digestion is another form of 

 work. There is, therefore, a continual demand for energy for 

 the internal work of the animal. But if the animal is called 

 upon to do additional (external) work, such as running or 

 hauling, an additional supply of energy is required. Animals 

 therefore require more food when they do external work than 

 when at rest. 



Matter can undergo various physical and chemical changes, 

 but the total quantity remains unchanged. In other words, 

 something cannot be produced from nothing. This funda- 

 mental law of nature is applicable to the changes which take 

 place in living organisms as well as to those in inanimate 

 substances. Animals cannot produce milk, or eggs, or fat, or 

 wool, or anything else, from nothing. All that they can do is 

 to transform the constituents of the food into the constituents 

 of these things. Only certain kinds of materials are capable 

 of undergoing such changes. Animals producing milk, or fat, 

 or any other substance, require more food than similar animals 

 which are not producing these things ; and the additional food 

 must be of suitable character. 



The food of animals consists of plants, i.e. of the chemical 

 compounds of which plants are made up. It is these com- 

 pounds that are used by the animal to repair the waste due to 

 oxidation ; they serve as fuel to maintain the temperature of 

 the body and to provide the energy required for the perform- 

 ance of work. It is by the transformation of these chemical 

 compounds into others that the mass of the animal is increased, 

 and that milk, wool, eggs, etc., are produced. 



Any substance that will burn will do to make a fire, but 

 some are more suitable than others. Coal, for instance, gives 

 a hotter and more lasting fire than twigs or paper ; but it may 

 be remarked in passing that if equal masses were compared, 

 the difference would not' be so great as is sometimes supposed. 

 In like manner, almost any oxidisable substance that the 

 animal can absorb will serve for those purposes in which the 

 food serves as fuel, e.g. to maintain temperature, to enable 



