266 LIFE AND DEATH. 



these analogies will in any way serve as explanations. 

 We should rather seek to derive the vital from the 

 physical phenomenon. This is the sole ambition of 

 the physiologist. To derive the physical from the 

 vital phenomenon would be unreasonable. We do 

 not attempt to do this here. It is nevertheless true 

 that analogies are of service, were it only to shake the 

 support which, from the time of Aristotle, has been 

 accorded to the division of the bodies of nature into 

 psucJiia and apsucJiia — i.e., into living and brute 

 bodies. 



§ 2. The Brownian Movement. 



The Existence of the Brownian Movement. — The 

 simplest way of judging of the working activity of 

 matter is to observe it when the liberty of the 

 particles is not interfered with by the action of the 

 neighbouring particles. We approximate to this 

 condition when we watch, through the microscope, 

 grains of dust suspended in a liquid, or globules of 

 oil suspended in water. Now what we see is well 

 known to all microscopists. If the granulations are 

 sufficiently small, they seem to be never at rest. 

 They are animated by a kind of incessant tremor ; 

 we see the phenomena called the "Brownian move- 

 ment." This movement has struck all observers since 

 the invention of the magnifying glass or simple 

 microscope. But the English botanist, Brown, in 

 1827, made it the object of special research and gave 

 it his name. The exact explanation of it remained 

 for a long time obscure. It was given in 1894 by 

 M. Gouy, the learned physicist of the Faculty of 

 Lyons. 



