METHODS 19 



equilibrium are bound together by relations of cause and 

 effect, it will happen in the long run that an external agent 

 will be able to produce in a colloid a result of a very different 

 dimension from its ow T n. A sound vibration, for example, 

 may determine secondarily a chemical modification from 

 having set the suspended particles in motion ; reciprocally, 

 a luminous vibration may determine secondarily a modification 

 of the colloidal state, from having directly produced certain 

 chemical reactions. And yet sound vibrations are too 

 great in dimension with respect to chemical phenomena, and 

 light vibrations, on the contrary, are too small with respect 

 to the particles of the colloids, to be able directly to pro- 

 duce that effect which they determine secondarily. 



Thus not only does life, if I may use the expression, 

 bestride two series of phenomena so widely separated as 

 sound vibrations and luminous vibrations on the one hand, 

 and on the other molecular and chemical reactions and 

 particle or colloidal variations ; but life also sets up a con- 

 nexion between these two series of phenomena, which should 

 seem utter strangers to each other. These are essential 

 facts, and we shall have to come back to them. 



