162 THE FEEDING OF ANIMALS 



from carbohydrates involves complex chemical trans- 

 formations not fully imderstood. 



FOOD AS A SOUECE OF ENERGY 



236. Work perfofmed by the animal organism. — 

 The living animal, either as a whole or in some of its parts, 

 is constantly in motion. This means that the animal 

 mechanism is ceaselessly performing work. Even if the 

 body is apparently quiet, the heart beats, pmnping 

 blood to all parts of the body, the limgs are expanded 

 and contracted, and the stomach and intestines keep up 

 the movements 'which are essential to digestion. Besides, 

 a living body is the seat of continuous, invisible and com- 

 plex chemical and physical changes that, if not work in 

 the common meaning of the term, are its equivalent. 

 Walking, trotting, pulHng, lifting, pumping blood, 

 breathing, masticating, digesting and assimilating food 

 represent, then, a great variety of operations of those 

 living machines which we have named horse, ox, cow, 

 and sheep. 



237. Work requires the expenditure of energy.— 

 Now work requires the expenditure of energy. The 

 projection of a rifle ball through space at the rate of 2,000 

 feet a second is work. The ball does not move of itself, 

 but is propelled by the application of the energy stored in 

 a powerful explosive. Back of every one of our great 

 mechanical operations, such as pumping, grinding, and 

 moving railroad trains, will always be found some sort 

 of energy, and what is true of machinery made of wood 

 and iron is equally true of that made of bone and muscle. 

 The fact that the mechanism is alive does not abrogate 

 a single physical law, so that the fundamental principles 



