With the addition of a phase sensitive detector and a discriminator circuit to the impedance bridge (Rothschild, 1948), counts of the impedance change frequency (icf) of a semen sample can be recorded on a mechanical counter. Further separate circuits to indicate balance of the bridge have been added so that the cathode ray tube of the original instrument is no longer needed for balancing or counting icf.
Highest icf counts were recorded when the concentration of ram spermatozoa lay between 9 and 12 × 108 spermatozoa/ml. Activity fell rapidly in more concentrated samples tested at 38° C unless the sample was simultaneously dialysed against an isosmotic buffered saline diluent containing fructose.
There were no significant differences between the performance of four electrodes tested, but icf was depressed by the presence of an electrode in the sample for 10 min at 38° C before a reading was taken.
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