Light-scattering studies of bull spermatozoa. II. Interaction and concentration effects

The complete autocorrelation function of the intensity fluctuations of laser light scattered from motile bull spermatozoa is shown to depend upon several factors not previously considered. Samples of bull spermatozoa generally contain a substantial proportion of dead cells, which give rise to slowly decaying components of the autocorrelation function. Whereas previous work has concentrated on the form of the fast decaying autocorrelation component, we are concerned here with the relative amplitude and shape of the slow autocorrelation component and the general form of the composite function. In principle, the relative amplitudes of the fast and slow components of the autocorrelation function can be used as an assay of the proportion of swimming cells. We show that this amplitude ratio depends upon cell concentration, scattering cell geometry, and scattering angle. A simple model is developed to explain these results on the basis of the asymmetry of light scattered from these cells, motile/immotile cell interactions, wall-swimming effects, and geotactic reorientation of dead cells.