146 FRANCIS D. CARLSON 



be selection in favor of those forms which have the most efficient mo- 

 tile mechanisms. 



This analysis can hardly be considered as complete, for it has 

 oversimplified the problem of diffusion to a moving cell, and stirring 

 in the environment, such as undoubtedly exists in nature, has been 

 neglected entirely. There are, however, a few new results that should 

 be emphasized. The first is the suggestion that fiagella may function 

 primarily as agents for stirring of the local environment and thus in- 

 crease the rate of influx of a required nutrient. Motility would in 

 this case be incidental. The second significant result is that, no matter 

 how inefficient the mechanism of motility may be, it is always possi- 

 ble to achieve a net gain in energy intake by moving. And finally, in 

 an environment with limited or decreasing" supply of essential nu- 

 trient, all other factors being equal, those organisms with the most 

 efficient motile mechanisms will tend to be selected for by virtue of 

 their ability to collect extra nutrient for growth at a higher rate. 



REFERENCES 



Chandrasekhar, S. 1943. Stochastic problems in physics and astronomy. 



Revs. Modern Phys., 15, 1-89. 

 Lamb, H. 1932. Hydrodynamics, 6th ed. Cambridge University Press, 



Cambridge, England. 

 Taylor, Sir Geoffrey, 1951. Analysis of the swimming of microscopic 



organisms. Proc. Roy. Soc. (London), A209, 447-461. 



