15 



nitrogen in addition. Very recent physiological researches have 

 clearly shown that the amount of work done in the animal body, 

 both in keeping up its own internal heat, and in exerting energy 

 outside it, is entirely due to, and varies with, the complete com- 

 bustion of the carbon and hydrogen only contained in its food, by 

 means of the oxygen inhaled in breathing ; and that it does not 

 depend upon the oxidation of muscular tissue, or of the nitrogen in 

 nitrogenous food. Nitrogenous food apparently simply increases 

 the oxidative power of the tissues of the body. 



Work is measured in what are called foot-pounds — a pound 

 weight raised to the height of a foot is known as a foot-pound. A 

 good day's work for an average man is about 1,085,000 foot-pounds, 

 or 484 tons raised to the height of one foot. The average daily 

 need of the adult body is 4,900 grains of carbon and 300 grains of 

 nitrogen. By the respiration of each adult, about Soz. of solid 

 carbon, in the form of carbonic acid, is thrown off daily. 



Animals then exhale the substances which are necessary for 

 the food of plants, while plants prepare from these substances what 

 is necessary for the respiration and food of animals ; and thus 

 the balance of Organic Nature is maintained. 



In man, muscle is the instrument by which the transformation 

 of energy is accomplished, not the material which is itself trans- 

 formed ; and although muscle acts under the direction of the will, 

 it does not derive its power of acting from the will any more than 

 a steamboat derives its power of motion from the steersman. 



Reviewing the relations between the various forms of Energy 

 in nature, we see : — (1) That where one is excited or exists, many 

 others are also set in action ; hence, probably, all are modes of 

 motion ; (2) That any one can be transformed either directly, or by 

 intermediate steps, into any other ; and (3) That none of them 

 can be produced but by some other as an anterior. We also see 

 that they act uniformly, i.e., according to fixed laws. The term 

 " Law of Nature," in its scientific sense, is simply the expression of 

 the ordinary uniformity with which certain sets of phenomena occur. 

 In all phenomena, the more closely they are investigated, the 

 more are we convinced that neither matter nor energy can be 

 created or annihilated. 



