160 The Feeding of Animals 



whence would the heat energy come in this case ? 

 From the combustion of the carbon. Somehow, when 

 it is deposited in the plant, there becomes stored in 

 this carbon, in a way about which we can only 

 theorize, what perhaps we may call the chemical energy 

 of the atom, which, when combustion occurs, is changed 

 into heat or molecule motion. From these phenomena 

 we learn that not only are there several forms of 

 energy, but that one form is transferable into another. 

 Perhaps another illustration may still further serve 

 our purpose. A small dynamo is being run by a pair 

 of horses working in a tread power such as is used 

 for threshing grain. The horses are constantly climb- 

 ing up a moving treadway and thereby communicating 

 motion to machinery. This motion is, by the dynamo, 

 converted into electricity, which, by passing through 

 the carbon film of an incandescent lamp and there 

 meeting resistance, is in part, at least, transformed into 

 heat. We have, then, in a chain, muscular effort, 

 motion of the mass (pulleys, wheels, etc.), electricity 

 and heat, all active energy and all transferable the 

 one into the other. This is a fairly good picture of 

 what goes on with the horse himself, externally and 

 internallj', in sustaining life and performing labor for 

 his owner. Back of it all, and this is what interests 

 us, is the animal's food. As a result of years of 

 patient investigation, it has become known that 

 through the combustion of the carbon compounds of 

 vegetable and animal origin, which serve as nutrients, 

 chemical energy may be transformed into those other 

 forms that are manifested in the activities of living 



