Flagellar Hydrodynamics

Sections 1 and 2 give a general overview of biofluiddynamic aspects of microorganisms possessing flagella and of related organisms, followed by more detailed accounts of (i) motions in eukaryotic flagellates (protozoans and algae), based on the propagation of “bends” along flagella with the characteristic “9+2” structure, (ii) motions in bacteria propelled by “bundles” of flagellar filaments of quite different structure, each driven by a “rotary motor” at its base. For analyzing all these motions, it is argued that a true “flagellar hydrodynamics” is now needed. This should replace the “flagellar dynamics” (representing the fluid medium by crude resistance coefficients) which hitherto has been universally used, but whose accuracy is insufficient for the modern microbiologist’s requirements. Mathematical methods are applied to initiate the development of such a flagellar hydrodynamics in § 3. Finally, in § 4, its conclusions are summarized in nonmathematical language.