Motion of Spermatozoa in Fluid Streams

Abstract

IT is generally accepted that spermatozoa constrained to move in a fine tube swim preferentially upstream (they exhibit positive rheotaxis) when a current is established in the tube¹. Rothschild² has shown that the orientation of dead sperm depends on the direction of the local velocity gradient (Fig. 1); because the head of the spermatozoon sinks more rapidly than the tail under gravity, organisms in the bottom half of a horizontal tube point head upstream while those in the top half point head downstream. Thus it was not at all clear why live spermatozoa should tend on average to swim upstream².