152 



THE CYTOLOGY 



LIFE-HISTORY OF BACTERIA 



It is often assumed that the swarmers of Proteus arc capable of exceptionally 

 active motility in a fluid medium. In fact, when totally immersed they swim 

 much less actively than Vibrio with its single, polar flagellum. The swarmers, 

 with their thousands of flagella, are notable for their ability to move upon a 



Fig. 67 

 THE EVOLUTION OF FLAGELLA 



A. Typhoid bacterium showing typical peritrichous, monofibrillar flagella (sih'er impregna- 

 nation). 



B. Electron micrograph of complex flagellum of spirillum. {Bv cotii'tesy of Miss P. K. Pease). 



solid surface which is no more than moist. Under these conditions I Ihrio 

 is entirely immobilised unless the film of fluid is deep enough to permit it 

 truly to swim. This observation, taken in conjunction with the evidence of 

 habitat, leads inescapably to the conclusion that the profuse, peritrichous 

 flagellation of Proteus and of certain sporing bacilli is an adaptation to life 

 and motihty, not in water, but in damp soil or decomposing organic matter. 



