ELEMENTARY VITAL PHENOMENA 271 



The above picture of the transformation of energy in living 

 substance is as incomplete as was that of metabolism. As in the 

 latter, so in the former, only the beginning- and the end- 

 components of the series are known. Energy enters the living 

 body as chemical energy, light and heat. Light and heat are 

 consumed in providing more chemical energy — light in splitting 

 up in plants carbonic acid, which has in itself very slight value in 

 respect to energy, into atoms of carbon and oxygen possessing free 

 affinities, heat in causing a re-arrangement in the labile compounds 

 •of living substance by an increase in intensity of the intramolecular 

 vibrations. Chemical energy is, therefore, the source of all other 

 forms of energy in the organism ; by its transformation there are 

 derived mechanical energy, light, heat, and electricity. In the 

 same proportion in which these are given out by the organism, 

 chemical energy disappears. Hence the end-products of life, 

 ■carbonic acid, water, ammonia, etc., possess extremely little 

 chemical energy ; into such the introduction of new energy from 

 the outside, in both light and chemical substances, is necessary, 

 in order to make available in the plant new potential energy in 

 the form of free affinities. These are the beginning and the end 

 •of the series. But what in detail are the complex transformations 

 in the living body, what forms of energy in each special case 

 proceed directly from the introduced energy, what intermediate 

 •and retrograde changes the chemical energy passes through, until 

 it leaves the body again in the form of mechanical movement, 

 light, heat and electricity — these are subjects that in great part 

 are still obscure. More light may be expected here with the 

 advance of knowledge regarding the more special metabolic 

 processes, for the transformation of energy cannot be separated 

 from metabolism. 



For convenience, in this chapter, the phenomena of changes of 

 :substance, of form, and of energy have been considered separately. 

 In reality, these three groups cannot be separated from one another, 

 for the possession of form and energy belongs to the essence of 

 .substance. Every change of substance is at the same time a 

 change of form and energy. This is inherent in the nature of our 

 ■conception of matter, and applies to living as well as lifeless matter. 

 What has been treated separately under these three heads is one 

 .and the same event merely looked at from different points of view. 

 In brief: All vital phenomena of a body are the expression of a 

 ■continual change of the substance of ivhich it consists. 



