Since the introduction of the concept of capacitation, numerous investigators have attempted to define the changes that spermatozoa undergo in the female reproductive tract. Studies utilizing light and electron microscopy have failed to show alterations in sperm structure following incubation in the rabbit uterus for periods up to 15 hr, a length of time sufficient to accomplish capacitation (Bedford, 1970). The loss of tetracycline fluorescence from spermatozoa in the oestrous uterus has been suggested as an indicator of capacitation (Ericsson, 1967), but it has since been shown conclusively that this theory can no longer be considered tenable (Vaidya, Bedford, Glass & Morris, 1969).
Changes in the net negative surface charge of rabbit spermatozoa during passage through the epididymis have been demonstrated by micro-electrophoresis (Bedford, 1963). This communication describes changes