Introduction 

 Flagellar Propulsion 



SIR JAMES GRAY 



Department of Zoology, Cambridge University, Cambridge, England 



Not so many years ago an interest in the mechanism of flagellar 

 movement was restricted to a very small group of biological special- 

 ists. Today it is attracting almost as wide a range of high-powered 

 scientific effort as any other biological problem; mathematicians, 

 physicists, chemists, and biologists all find common ground. And so, 

 if some omniscient body were to tell me exactly how such systems 

 work, I would feel very embarrassed; the answer would involve a 

 knowledge of hydrodynamics and biochemistry far beyond my com- 

 prehension. But, from time to time is is useful to take stock of what 

 we know and consider how to collect more information. The pro- 

 ceedings of this symposium fulfill this need and provide the stimulus 

 for further effort. 



If we visualize the tail of a spermatozoon as a piece of aquatic pro- 

 pulsive machinery, three questions at once arise. (1) What are the com- 

 position, shape, and mutual relationship of each part of the prime 

 mover or engine? (2) What is the nature of the fuel, and how is its 

 chemical energy made available for useful work? (3) What are the pre- 

 cise shape, path of motion and frequency of movement of the pro- 

 peller surface? One cannot approach any of these questions without 

 realizing how far we have yet to go to find a comprehensive answer, 

 but at the same time feeling that we are steadily, if slowly, moving 

 in the right direction. The following notes deal almost solely with 

 the third and simplest of these three questions. 



THEORY OF FLAGELLAR PROPULSION 



The propulsion of nearly all living organisms depends on the princi- 

 ple that periodic changes in the form of the body take place against a 



