GROWTH 163 



growing crystal will conform and must conform to its en- 

 vironment. It is determined by physical law that copper 

 sulphate molecules will not arrange themselves in the crys- 

 talline form without a definite amount of water; if the 

 amount of water be excessive or deficient the copper sulphate 

 molecules, having always the same attraction for one an- 

 other, will still be unable to obey it, to approach one an- 

 other, and to arrange themselves in their due order. The 

 crystals of the same substance will be small or large accord- 

 ing as they are formed fast or slowly. And what is true of 

 the behavior of one substance alone in solution in another 

 is also true of many substances together in solution, 

 whether these find themselves in a cell or wholly outside a 

 living body. The molecules of the different substances will 

 mutually attract or repel one another, they will be indiffer- 

 ent or they will decompose one another, and when a state 

 of balance is attained, the molecules which result from all 

 the changes will arrange themselves in their characteristic 

 ways. Because the living protoplasm itself is composed of 

 molecules forming a definite structure, this structure, like 

 the whole crystal, is subject to physical infiuences, and its 

 component molecules are obedient to physical laws. So the 

 molecules and groups of molecules forming the living proto- 

 plasmic structure are pulled down by gravitation. The 

 molecules vibrate with lesser amplitude and draw together 

 in cold, vibrating with greater amplitude and so tending to 

 move apart when warmed. And as warmth makes molecu- 

 lar movements in any substance freer, so water makes pos- 

 sible still greater freedom of molecular movement in those 

 substances which dissolve in it. There are substances, how- 

 ever, which neither repel water as do the fats and oils, nor go 

 into solution in it as do many salts, but which still absorb 

 water in great quantity. This absorption results in greater 

 freedom of molecular and even of massive movement. Pro- 

 toplasm is one of these substances ; it swells as it absorbs 

 water, and its circulation, as well as its molecular move- 

 ments, becomes more rapid, up to the optimum. If still 

 more water is forced into it, the molecules and groups of 

 molecules composing it will be forced so far apart by the 



