674 ANNUAL REPORT OF THE OfE. Doc. 



thing analogous to the coal with which we started and containing 

 energy in the potential form. In a general way we may say that it is 

 theoretically possible to convert any form of energy into any other 

 form. 



Owe more very important fact regarding energy remains to be 

 noted. In all these changes and transformations, no energy is de- 

 stroyed. Energy, like matter, is indestructible. Take again the 

 case of the pile driver; when the weight is raised, a definite amount 

 of energy is expended in raising it and becomes potential in the 

 weight. Whctt the weight falls back to its original position, it gives 

 out exactly the same amount of energy which w-as imparted to it 

 when it was raised. In the swinging pendulum, the kinetic energy 

 at the lowest point is exactly equal to the potential energy at the 

 highest point and to the sum of the two at any intermediate point. 

 The potential energy of the water in the reservoir is represented ex- 

 actly by the amount of work which it took to raise that water to the 

 level which it has acquired, and it gives out exactly this amount of 

 energy in falling again to its original level. In the case of the coal, 

 it took exactly the same amount of energy in the sun's rays in the 

 carboniferous period to build up the organic substances of which the 

 coal is composed which is given off in the form of heat when that 

 same coal is burned. Any exceptions to this law of the conservation 

 of energy are only apparent and the more carefully we trace up the 

 track which the energy takes the more fully do we find it accounted 

 for. 



Thus far we have been dealing in general principles and with 

 facts which seem somewhat remote from the particular subject of 

 this paper. Let us come now to the application of them to the prob- 

 lems of animal nutrition. 



Bearing in mind the facts already stated, whenever we see work 

 being done, we shall look for the energy which accomplishes it aod 

 shall expect to see the principles which have just been expounded 

 hold true. When we look out on a crowded city street, we see in 

 the aggregate a very large amount of work being done by men and 

 animals. Whence comes the energy which accomplishes this work? 

 It comes, in the first place, as it does in the case of the steam en- 

 gine, from a combustion. Every animal is constantly giving off 

 substantially the same i)roducts of combustion which are given off 

 from the chimney of the steam plant or the stack of the locomotive, 

 namely, carbonic acid and water. The analogy of animal respira- 

 tion to combustion was first pointed out by Lavoisier, the French 

 discover of oxygen, who first supposed that this combustion took 

 place in the lungs of the animal, which he compared to a furnace. 

 Later, however, he adopted the view which is now universally held, 

 that this combustion takes place throughout the tissues of the liv- 



