HOW PHENOMENA ARE INTERPRETED. 73 



tion between the energy of food and bodily activity of every 

 kind ; that no more comes out of the bodily machine in the 

 shape of work, physical or mental, than is physically provided 

 by the foods digested. So vital force as an agency in living 

 things is as mythical as the other forces I have described as 

 non-existent. An explanation, then, of the phenomena of life 

 as manifested in either plant or animal is complete when the 

 physical and chemical antecedents have been presented in 

 their order and quantitative relations. There appears to be no 

 reason for holding to the view that there is anything more 

 mysterious or different in kind in so-called vital phenomena 

 than there is in what goes on in a test tube in a physical 

 laboratory. There may be a difference in complexity, not in 

 agencies. 



Of course everybody knows of what is called the conserva- 

 tion of energy which implies, as I have said already, that the 

 quantity of energy in the universe is constant, and when any 

 given kind appears, it is always at the expense of some other 

 kind which has disappeared, and the two are equal. If the 

 quantity of matter is not variable, and that is precisely what 

 all experience affirms, and if the quantity of energy is also not 

 variable, though its forms may be, then the apparent logic of 

 the case is that one of the factors of energy must be the 

 variable, and in fact energy as we know it is always a product. 

 It does not exist as an entity. One cannot assume that the 

 energy of a moving rifle bullet can be detached from it, so 

 as to enable one to hold the bullet in one hand and the energy 

 in the other. The variable factor is simply the rate of motion 

 the bullet may have, and this rate of motion, whatever it may 

 be in a given case, had its antecedent in some other body which 

 lost the motion which was imparted to the bullet. If this be 

 applied in every case, then it seems that every kind of phenom- 

 enon involving physical energy and every phenomenon does 

 involve such energy must be due to changes in the kind and 

 direction and amount of motions a body may have ; and there is 

 no reason for imagining or supposing in any given case the 

 existence or activity of any agency differing from or related 

 to those forms of energy which are investigated in physical 



