80 ORIGIN AND NATURE OF LIFE 



which he is dealing produce a stereotyping 

 effect on the mind, and unless the student is 

 always on the alert, he is apt to come to 

 believe that the atom is what the symbol 

 represents it to be, a fixed or motionless 

 structure, whereas it is in reality a centre 

 of ever-moving energy. It is by virtue 

 of its dynamical power that it undergoes 

 chemical transformations with building up or 

 breaking down of chemical compounds. 



Within the limits of ordinary chemical 

 reaction no changes of sufficient violence 

 occur to invade the energy equilibrium of 

 the constituent groups of electrons constitut- 

 ing the atoms, so the atom may be regarded 

 as stable, indestructible, and indivisible in the 

 sense explained in the previous chapter. 



The atom may accordingly be accepted by 

 the chemist as a working unit just as the 

 biologist still accepts the living constituent 

 cell of the plant or animal as a biological 

 unit, and the facts of the preceding chapter 

 need no more invalidate this position, than 

 the corresponding fact in quite modern biology 

 that many of the properties of the cell may 

 be carried on by isolated parts of the cell, 

 which a few years ago were only considered 

 possible for the entire and undivided cell to 

 perform. 



