74 PRELIMINARIES TO FERTILIZATION 



Beck, Cupps, and Elliott, 1943; Chang, 1946a,b; Emmens and 

 Swyer, 1948; Cheng, Casida, and Barrett, 1949; Rothschild, 

 1951b; Willett, 1953; Bishop, 1954). Excessive dilution in vitro 

 is invariably harmful, probably because of the irreparable decay 

 of enzyme systems in the actively metabolizing cells resulting 

 from the stimulating effect of dilution, and because of loss of 

 substances from the cell surface (Emmens and Swyer, 1948). In 

 particular, it is known that electrolytes remove phospholipid ma- 

 terial from cell membranes ( Milovanov, 1934a,b; Lovelock, 1954, 

 1955; Dallam and Thomas, 1952). The efficiency of removal 

 varies with the electrolyte, according to the lyotropic series of 

 ions (Anderson, 1945). It seems probable that the functions of 

 the osmotically active organic constituents of the seminal plasma, 

 such as fructose, lactic acid, citric acid, amino acids, urea, and 

 inositol, include maintenance of a suitable osmotic environment 

 with a low electrolyte to nonelectrolyte ratio. Kampschmidt, 

 Mayer, and Herman (1953) and Kok (1953) have found that the 

 survival of spermatozoa in vitro is prolonged when the electro- 

 lyte to nonelectrolyte ratio of the diluents is reduced by the ad- 

 dition of metabolizable sugars, and Roy and Bishop ( 1954 ) have 

 obtained similar results by replacing electrolytes with glycine. 

 Although other explanations can be offered, it is likely that the 

 beneficial effect of the sugars and glycine was due to reduction 

 of the stimulating and destructive action of the electrolytes. With 

 sea urchin spermatozoa, on the other hand, glycine provides pro- 

 tection chiefly by chelating heavy metals (Tyler and Rothschild, 

 1951; Tyler, 1953). Substances such as lecithin, albumin, mucin, 

 and egg yolk also help to protect the spermatozoon membranes 

 from the deleterious effects of dilution: constituents of the semi- 

 nal plasma and of the female genital secretions presumably have 

 a similar function. 



It would seem, therefore, that the genital secretions, both of 

 male and female but chiefly the former, have the function of ac- 

 tivating the spermatozoa in a controlled manner, the stimulating 

 property being appropriately balanced by the property that miti- 

 gates the deleterious effect of electrolytes. 



