158 The Feeding of Animals 



the term, are its equivalent. Walking, trotting, pull- 

 ing, 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. 



Now work requires the expenditure of energy. The 

 projection of a rifle ball through space at the rate of 

 two thousand feet per 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 of energy as 

 applied to machines are as fully applicable to the activ- 

 ities of animal life. 



It is safe to go farther, and say that the animal 

 organism does not originate energy. Among the fun- 

 damental conceptions upon which all our knowledge 

 of chemical and physical laws rests is this, that energy 

 and matter are indestructible, and, moreover, that the 

 sum total of these in the universe is unchangeable. 

 If, then, the horse expends the muscular energy neces- 

 sary to draw a load of one ton over ten miles of road, 

 the equivalent of this must have been supplied to his 

 body from some outside source. He could not create it. 

 We know that this is so, and we also know it is con- 

 veyed to the animal in the food. 



I 



