40 WHAT IS LIFE 



in some measure chemical, that is to say chemical 

 changes and operations take place during its pro- 

 gress. But when one says so much one is not 

 saying that the changes are purely chemical, for 

 such, in fact, is not the case. In the course of an 

 ordinary chemical combination two or it may be 

 more substances unite to form a third, as common 

 salt, for example, is formed from sodium and hydro- 

 chloric acid. But the cell takes up not-living 

 matter and assimilates it and converts it into liv- 

 ing protoplasm. Moreover this process of growth 

 is interstitial in its character and not superficial, in 

 other words it is not a growth in size due to the 

 deposition of new layers on top of the old ones, as 

 in the case of a rolling snowball. The deposition 

 of new material occurs throughout the entire sub- 

 stance of the cell, so that its increase in size is 

 due to a general expansion of the entire organism. 

 Crystals and And herein lies a prime difference between the 

 ring things jj v j n g or g an i sm an( j a crystal, forms between which 



some have urged that a close resemblance exists, 

 or at least have argued that between crystallisation 

 and assimilation there were sufficiently close re- 

 semblances to permit it to be argued that there 

 was no fundamental difference between the two 

 processes. The difference just mentioned is funda- 

 mental in character and sufficient in itself to 

 distinguish the two processes. But beyond this 



