82 The Biochemistry of Semen 



reasonable period at the low temperatures of storage in vitro. There 

 is also the problem as to whether semen should be stored in a 

 diluted form or whether it would be better to dilute it just before 

 actual use. It would appear that on the whole, under natural in vivo 

 conditions, spermatozoa survive best in a highly concentrated state 

 when their motility is reduced to a minimum; the prolonged life-span 

 of sperm in the epididymis certainly points in that direction. Another 

 even more suggestive example is the behaviour of ejaculated bat 

 sperm: the density of sperm as found in the bat uterus after copula- 

 tion is very high, about 6 million cells //^l. (Schwab, 1952); in this 

 condition the spermatozoa seem to be largely immotile, but are 

 nevertheless capable of survival for several months. Such spermato- 

 zoa respond to artificial dilution by becoming intensely motile, but 

 then they survive for not longer than a few days. 



