104 life and death. 



§ 2. First Law of Biological Energetics. 



It is easy to understand, after these remarks, the 

 significance and the scope of this assertion which 

 contains the first principle of biological energetics — 

 namely, that the phenomena of life have the same 

 claim to be called energetic metamorphoses as the 

 other phenomena of nature. 



Irreversibility of Vital Energies. — However, there 

 is one characteristic of vital energies which deserves 

 the closest attention. Their transformations have a 

 direction which is in some measure inevitable. They 

 descend a slope which they never re-ascend. They 

 appear to be irreversible. ' Ostwald has rightly in- 

 sisted on this fundamental characteristic, which no 

 doubt is not that of all the phenomena of the living 

 being without exception, but which is certainly that of 

 the most essential phenomena. There are reversible 

 phenomena in organisms ; there are energetic trans- 

 formations which may take place from one form of 

 energy to another, or vice versa. But the most 

 characteristic phenomena of vitality do not act in 

 this way. We shall presently see that most functional 

 physiological acts begin with chemical and end with 

 thermal action. The series of energetic transforma- 

 tions takes place in an inevitable direction, from 

 chemical to thermal energy. The order of succession 

 of ordinary energies is thus determined in the machine 

 of the organism, and therefore by the conditions of 

 the machine. The order of transformation of vital 

 energies is still more rigorously regulated, and the 

 phenomena of life evolve from childhood to ripened 

 years, and thence to old age, without a possible 

 return. 



