IV THE CELL AND THE ORGANISM 67 



Unlike any other substance in nature, the protoplasm of 

 the cell is vitally active and is in an incessant process of real 

 creative change; parts are continually being destroyed and 

 replaced by new protoplasm which is continually being 

 formed. No other substance has this power of making its 

 own material, so to say. A crystal, for instance, builds itself 

 up from its own material already existing in solution without 

 any change being made in its constitution. The crystal 

 serves merely as an attractive centre round which its 

 material, already present in dissolved form, may be 

 deposited in solid form. With protoplasm the process of 

 growth or renewal is quite different. The material taken 

 in is entirely altered and recombined into the substance of 

 which the protoplasm is composed, and this material, so 

 altered and transformed, is then by some yet unknown 

 process taken up and assimilated into the protoplasm or 

 living substance of the cell. This complete transformation 

 and this mysterious assimilation of its material is one of 

 the most unique functions of the cell, and its far-reaching 

 significance will later on be more particularly stressed. 



The technical name for this complete transformation which 

 the cell effects in the material it takes in is metabolism, and 

 it may therefore be said that metabolism is the process which 

 above everything distinguishes living from non-living matter. 

 The cell is not a static or stationary organism; it is for ever 

 being built up by new material which it transforms into its 

 substances, and it is for ever being broken down through 

 the new cell substances which it forms and gives off in order 

 to build up the various parts of the complete plant. And the 

 activity by which the material is taken in in one form, then 

 transformed and assimilated into the substance of the cell, 

 and then again given off as different cell substances for the 

 building up of the various parts of the plant — this activity, 

 while apparently a series of chemical and physical processes, 

 implies a co-ordinated system which is unlike anything seen 

 in the purely physical or chemical domain. The physical 

 and chemical changes seem to be merely the mechanisms or 

 instrumentalities used by a deeper organic process, which 



