62 THE NATURE AND ORIGIN OF LIFE 



seldom fully realized in nature. For the most part it is 

 accompanied by circumstances that superpose destructive 

 reactions on the assimilative reactions and thus cause 

 variations. 



Strictly speaking, therefore, we do not often meet in 

 nature with a phenomenon of elementary life manifesting 

 itself, Sit least, not in its purity. In a being that lives there 

 are at the same time phenomena of life and phenomena of 

 death ; and the being remains alive only so long as the phe- 

 nomena of death do not carry the day over the phenomena 

 of life. In other words, the phenomena which take place 

 in a living being can but rarely be translated into the exact 

 formula : 



a + Q \a + R. 



For an exact account of what takes place we have to 

 combine with this first formula of elementary life as it 

 manifests itself one or more formulae of reactions destruc- 

 tive of the form : 



a + B = C + D. 



Of course, this is factitious decomposition ; but it is 

 convenient in analysing the complex facts of life. We 

 shall see later that, with a higher class of beings in whose 

 life we observe periods of work and repose, there is not 

 always superposition, but the alternation of Conditions 

 No. 1 and No. 2. And, although it is contrary to a very 

 widespread opinion, Condition No. 1 corresponds with the 

 periods of work, whereas the greater number of physiolo- 

 gists admit with Claude Bernard the wear of living sub- 

 stances in their work functional destruction. This error 

 will be made clear in the next part of our book by using 

 the rational method of decomposition into functions ; 

 it results chiefly from the existence, in the midst of 

 living substances that are really active in the biological 



