74 The Biochemistry of Semen 



the motility and prolongs the life of the spermatozoa (Scheuring, 

 1928). Trout spermatozoa have been a favourite object for investi- 

 gations on the action of various cations and anions on sperm moti- 

 lity (Scheuring, 1928; Gaschott, 1928; Schlenk, 1933; Schlenk and 

 Kahmann, 1938). Among the many facts brought to light by these 

 investigations, the effect of potassium ions merits particular atten- 

 tion. In contrast to sodium chloride, a diluent containing 01 5% 

 potassium chloride was found to have no activating effect on sperm 

 motility, and moreover, the addition of potassium ions to a suspen- 

 sion of motile sperm in sodium chloride, rendered them motionless. 

 This inhibition by potassium ions, however, was shown to be 

 reversible since even after prolonged storage of sperm in the pre- 

 sence of potassium ions, it was still possible to restore their motility 

 by dilution with water or sodium chloride solutions. The fact that 

 trout spermatozoa show great activity upon dilution with water or 

 sodium chloride solution but not with trout seminal plasma, has 

 been attributed by Schlenk to the high potassium content of the 

 latter (80 mg./lOO ml.); in his view, the rapid increase of motility 

 after dilution with water should be ascribed to the decrease of potas- 

 sium concentration in the seminal plasma and the passage of potas- 

 sium ions from the sperm cells into the surrounding medium. 

 According to this interpretation, potassium ions fulfil a double 

 function in semen: they preserve the sperm energy by inducmg 

 quiescence, but at the same time, they engender, as it were, a state 

 of preparedness ('Bewegungsbereitschaft'). 



Much information on the effect of dilution has been gathered 

 from experiments with sea-urchin semen. The spermatozoa of sea- 

 urchins, unlike those of man and higher animals, are immotile in 

 the absence of oxygen (Harvey, 1930; Barron, 1932). In sea-urchin 

 semen which generally has a high sperm density (there are some 

 2x10^° cells /ml. in Echinus esculentus), the spermatozoa are 

 motionless so long as they remain undiluted, but when shed into 

 or artificially diluted with, sea-water, they become intensely motile 

 and with increasing dilution their oxygen uptake rises as well (Gray, 

 1928, 1931). The lack of sperm movement in undiluted sea-urchin 

 semen has been regarded by Gray as the outcome of mechanical 

 overcrowding; each cell exercising a restraining or allelostatic effect 

 on the activity of its neighbours. Other authors believed the lack 



