Chemical and Physical Properties of Semen 41 



remembered, rest on the assumption that although light is absorbed 

 both by sperm and seminal plasma, the scattering of light is due 

 exclusively to the former, so that only light-scattering as such, is 

 related directly to sperm density. In practice, the light-scattering and 

 light-absorption due to the spermatozoa predominates so much 

 over the light-absorption of the seminal plasma that under properly 

 controlled conditions the error due to the presence of the latter can 

 be neglected. This applies certainly to the semen of sea-urchin, bull 

 and ram, but need not necessarily be true of other species, in which 

 the seminal plasma itself shows a considerable degree of opaqueness. 

 Furthermore, the spermatozoa present in a given ejaculate may 

 differ in their light-reflecting capacity, apparently in proportion to 

 the degree of sperm 'ripeness' and thereby, of fertility (Lindahl 

 et al, 1952). The light-reflecting capacity of the sperm cell may 

 also be related to another optical change associated with sperm 

 ripening, namely the increase in 'luminosity' of the sperm surface 

 in dark-field illumination. 



It has been claimed that the spermatozoon possesses at the head 

 and tail small, but directly opposite, electrical charges. However, 

 all that can be claimed with certainty is that an electric charge is 

 associated with the sperm cell but that its sign and magnitude depend 

 largely on the concentration of the various positively and negatively 

 charged ions in the surrounding medium. The following values for 

 electro-conductivity in semen at 25°, expressed in reciprocal 

 ohmsxlO"*, were given by Bernstein and Shergin (1936): bull 

 89-5-116-3, ram 48-5-80-5, stallion 111-3-129-5, boar 123-3-134-6, 

 rabbit 85-5-101 -4; and by Zagami (1939): man 88-107 (at 20°), and 

 dog 129-138. 



Much scientific interest and practical importance in the rating of 

 semen quality attaches to the characteristic periodic changes in 

 electrical impedance which occur in semen samples with high sperm 

 density and motility, and which have been shown by Rothschild 

 (1948^, 1949, 1950a) to be associated closely with the so-called 

 'wave motion' of the spermatozoa. When a drop of ram or bull 

 semen of high density is placed on a microscope slide and examined 

 at 37° under low magnification, a characteristic phenomenon can 

 be observed in the form of slow, periodically appearing bands of 

 high opacity or 'waves'. Measurements by means of the impedance 



