introduction: flagellar propulsion 11 



forces exerted by flagella 



The efficiency of a propulsive system can be assessed by the 

 amount of useful work performed per unit expenditure of fuel. 

 There seems no immediate prospect of reaching such an estimate for 

 flagella by direct observation although the work of Yoneda (1960) 

 on the forces exerted by a single cilium might perhaps form a basis 

 for reasonable approximation. Calculations of forces or of work 

 done, which are based on the assumptions at present underlying the 

 general theory of propulsive speeds, must be accepted with caution; 

 they are not only suspect for the reasons already alluded to, but also 

 because they depend on the absolute value of the tangential drag 

 coefficient about which there is considerable uncertainty. 



An alternative approach to an estimate of the forces involved in 

 flagellar activity might perhaps be derived from a study of the di- 

 rection and velocity of displacement of very fine particles in the 

 vicinity of the moving filament, in other words, from an extension 

 of the earlier work of van Trigt (1919) and Lapage (1906). How 

 far, if at all, such observations might be expected to lead to quanti- 

 tative conclusions must be judged by hydrodynamical experts. 



Experimental measurements of useful propulsive effort would be 

 of limited value unless accompanied by information concerning the 

 amount of chemical energy necessary to maintain a given amount of 

 mechanical effort. The accuracy of any such estimate might well 

 depend on whether the amount of metabolic activity necessary to 

 maintain mechanical effort is large or small compared with that 

 necessary to maintain other active processes within the cell which 

 are not directly concerned with movement. These are problems for 

 biochemists. 



These rather discussive remarks might not inappropriately end 

 where they began, by emphasizing flagellar movement as a most 

 happy and fruitful field for cooperative effort. 



REFERENCES 



Blokhuis, E. W. M. 1961. Optical investigations on the movement of bull 

 spermatozoa. Proc. IV Intern. Congr. on Animal Reproduction, pp. 

 1-6. 



