The Influence of Extraneous Factors 61 



up eosin whereas live cells remain unstained. The time required to 

 reach the 50% mortality level was stated to be 6 hr. at pH 6-4-6-5, 

 29 hr. at pH 7-2-7-9, 15 hr. at pH 8-5-9-5, 7 hr. at pH 9-7-9-8, and 

 4 hr. 30 min. at pH 10-2. 



However, even after spermatozoa have been rendered immotile 

 by excessive acidity they can still be resuscitated by alkalinization, 

 always provided that the exposure to acid has not been unduly 

 long(Engelmann, 1868; Lillie, 1913, 1919; Gray, 1915; Muschat, 1926; 

 Schlenk, 1933). Under conditions in vitro, the time intervals at which 

 the sperm can be revived, correlate well with the mortality rate 

 (Emmens, 1947); no reactivation was seen when the death rate of 

 rabbit sperm exceeded 80%. 



The slowing down effect of weak acids and the reactivating in- 

 fluence of weak alkalis may well be of some importance for the 

 activity of spermatozoa in vivo, in the various parts of the male and 

 female reproductive tract. There are, however, several other im- 

 portant factors which influence sperm motility and survival in vivo, 

 such as the concentration of various ions and nutrients, dilution, 

 and the tension of oxygen. Thus, in the epididymis, and partly also 

 in the vas deferens, the spermatozoa are immotile at a pH which 

 approximates neutrahty (Lanz, 1929; Bishop and Mathews, 1952); 

 here, presumably, the combination of the very low oxygen tension, 

 deficiency of carbohydrate and limitation of space acquires greater 

 significance than the hydrogen ion concentration. 



Tonicity as a sperm-affecting factor ranks equal in importance 

 with the hydrogen ion concentration. Most investigators of semen, 

 including Yamane (1920), Gellhorn (1922, 1924, 1927), and Milo- 

 vanov (1934), agree that on the whole, spermatozoa seem to be 

 immobilized much more readily by hypotonic than hypertonic, 

 diluents. However, it must be remembered that the ultimate effect of 

 tonicity depends upon certain other prevailing conditions. Thus, 

 for example, Emmens (1948) who studied the motility of rabbit 

 spermatozoa at various pH values with diluents of different chemical 

 composition and tonicity, has shown that at pH 5 •8-6-6, the sperma- 

 tozoa were more sensitive to hypotonicity than to hypertonicity, but 

 in an alkaline medium the situation was reversed. In an analogous 

 study of ram, bull and human spermatozoa (Blackshaw and Emmens, 

 1951) it was established that at all pH levels, hypertonic solutions 



