THE MECHANISM OF LIFE 477 



I. The Vital Process 



As previous treatment of this subject has shown,^ our knowledge 

 of the individual events in the metabolism of living substance 

 is unfortunately thus far very meagre. Investigation of the 

 mechanism of the physical phenomena of life is necessarily still 

 far from complete, and progress can be made only slowly. An 

 essential advance in this direction can be expected only from the 

 detailed study of the processes in the cell, for the cell is the place 

 where the vital process itself has its seat, and where all vital 

 phenomena occur in their simplest form. Not until the physiology 

 of organs, which is able to explain only the gross performances of 

 the complex cell-community, develops into cell-physiology, can we 

 hope essentially to enlarge our knowledge of the more delicate 

 mechanism of life. Thus far only the first steps have been taken 

 in this direction. 



If, therefore, we attempt to form, so far as possible upon the 

 basis of our present knowledge, a picture of the vital process in 

 living substance, it can be only a sketch in which the most general 

 elements are indicated in gross outline. Notwithstanding this, 

 some kind of a picture of the vital process is necessary for further 

 systematic investigation. 



A. THE METABOLISM OF BIOGENS 



1. Bio gens 



It has been seen in a previous chapter that, in general, the 

 characteristic of living organisms in comparison with those dead 

 or apparently dead consists in their metabolism, the expression 

 of which constitutes the vital phenomena. It is necessary to go a 

 step beyond this general fact. 



It will be recalled that in the determination of the chemical 

 compounds that constitute living substance investigation deals 

 exclusively with the dead cell. For the completion of a picture 

 of living substance two questions now remain to be answered, viz. : 

 first, do the chemical compounds which are found in the dead cell 

 occur as such in the living cell ? and, second, are there in the 

 living cell still other compounds which are not present in the dead 

 cell, which, in other words, are bound up inseparably with the life 

 of the cell ? 



The first of these questions is relatively easy of answer. A 

 careful comparison especially of the solid bodies that may be found 

 as reserve-substances for a time unchanged in the living cell, with 

 the corresponding substances of the dead cell shows that there 



1 Cf. p. 157. 



