172 



PHYSIOLOGY OF MICROORGANISMS 



BROWNIAN MOTION 



This phenomenon is familiar to students of microbiology. When 

 studying some bacteria in a hanging-drop under one-twelfth oil immer- 

 sion objective, this movement may be seen. It is not only visible with 

 some of these living organisms but extends to many substances existing 

 in very fine particles and suspended in certain media. It is a common 

 phenomenon among colloidal solutions. 



FIG. 105. Illustrating Brownian movement (After Perrin). 



The character of the movement is well illustrated by Perrin* (Fig. 

 105) who has made a special study of the subject. The path is a 

 straight line until opposed when it rebounds in another straight line 

 producing a zig-zag route. 



The cause of the motion appears to be inherent in the molecular 

 movements of the dispersion means of a colloid, of the liquid in which 

 the particles are suspended. The direction of the particles as stated 

 above, is that of a straight line until a collision with the invisible mole- 

 cules takes place when the rebound sends the .particles in a straight line 

 in another direction. This process continues indefinitely. The 



* Perrin, M. Jean, Brownian Movement and Molecular Reality. 



