42 The Biochemistry of Semen 



bridge make it possible to assess this characteristic sperm movement 

 in a more objective and quantitative manner than by visual esti- 

 mates; but they can only be made with semen samples which are 

 sufficiently dense to show the 'wave motion'. Assays carried out 

 with the electrical method in the semen of bulls at several British 

 Artificial Insemination Centres revealed an interesting correlation 

 of impedance change frequency with the conception rate (Bishop 

 et ai, 1954). 



Distinct from the wave-motion or locomotion 'en masse' (Walton, 

 1952) is the movement of individual spermatozoa which in highly 

 motile semen takes the form of so-called 'forward' or 'progressive' 

 motility, but which in poor specimens is confined to side-to-side 

 'oscillatory' movements (Plate IV). Recently, there have been several 

 attempts to replace the subjective and semi-quantitative microscope 

 appraisals of motility by more clearly defined methods, of which 

 those by Bosselaar and Spronk (1952) and Rothschild (1953a, b) 

 deserve special mention. 



Viscosity, specific gravity, osmotic pressure, and ionic equilibrium 



The viscosity of whole semen depends largely upon the concen- 

 tration of spermatozoa. Thus for example, the viscosity of bull 

 semen (relative to that of pure water which is taken as unity) can 

 vary from 1-76 in a specimen containing 80,000 sperm/ywl. to 10-52 

 in a sample with 2,260,000 sperm //^l. (Szumowski, 1948). Seminal 

 plasma itself, seldom exceeds in bulls a relative viscosity value of 2 

 but higher values have been recorded in other species, especially 

 those which exhibit the phenomenon of gelation. 



The average specific gravity of whole semen is 1028 in man, 

 1-011 in dog, and 1-035 in bull, with fluctuations due in the first 

 place to the variable ratio between sperm and seminal plasma. The 

 latter is so much lighter than the spermatozoa that in practice the 

 specific gravity of semen is often found to be directly proportional 

 to sperm concentration. In bull semen, low specific gravity is usually 

 associated with low sperm concentration and poor 'quality', whereas 

 high values accompany good density and good 'quality' (Anderson, 

 1946(7). This is not surprising in view of the fact that the specific 

 gravity of bull seminal plasma is not greater than that of blood 

 plasma, whereas the average specific gravity of bull spermatozoa 



