The stirring of the medium by bull spermatozoa

1. Bull semen diluted 1/5 or 1/10 respired at the same rate whether the manometers were stationary or shaken. 2. Respirometric experiments using a manometer flask of special shape showed that bull sperm suspensions achieve this result by increasing the effective diffusion coefficient of oxygen in the suspending medium by 900%. 3. The hypothesis is put forward ( a ) that these results are caused by the existence of short-range order, as opposed to disorder, in bull sperm suspensions, even at comparatively low sperm densities (dilution 1/8 to 1/20); ( b ) that this order produces group sperm velocities greater than those of isolated spermatozoa; and ( c ) that as a result, larger volumes of the suspending medium are convected with the ordered sperm groups, causing an augmented ‘diffusion’ of oxygen. 4. This hypothesis was examined by taking photomicrographs of sperm suspensions at different dilutions and temperatures and determining from them the distributions of (i) the distance between pairs of nearest spermatozoa; (ii) the angle of inclination of a sperm head relative to that of the spermatozoon nearest to it; and (iii) the relative position of the nearest spermatozoon. 5. Comparison of the observed distributions and the corresponding random ones showed that the spermatozoa attracted each other, so that transient sperm groups were formed, in which the spermatozoa tended to swim in the same direction. A reduction in temperature or sperm density decreased the sperm order.