34 



The Biochemistry of Semen 



Table 5. Individual variations in the level of fructose in semen 

 (Ejaculates collected at weekly intervals.) 



characteristic chemical component of rabbit semen, is found largely 

 in the gel, and its varying content reflects the variability of the 

 latter (Fig. 6). 



Frequency of ejaculation also affects the composition of individual 

 samples of semen. Table 6 shows the results of a so-called exhaustion 

 effect on the semen of a bull (Mann, 1948«); in this experiment, eight 

 ejaculates were collected from the same animal within 63 min., at 

 7-10 min. intervals. As a result of the multiple collections, the sperm 

 density fell from 1,664,000 cells///l. in the first, to 98,000 cells/^ul. 

 in the last, ejaculate. This decrease, however, was not accompanied 

 by a corresponding diminution of fructose concentration, which was 

 much the same in the first (760 mg./lOO ml.) and last (690 mg./lOO 

 ml.) ejaculate. But it must be remembered that the seminal vesicles 

 of a bull differ from those of man and other mammals by their 

 exceptional capacity: in some bulls it is possible to recover up to 

 50 ml. of secretory fluid from the seminal vesicles, enough to provide 

 at least a dozen fructose-rich ejaculates. 



