Chemical and Physical Properties of Semen 35 



Table 6. Ejfect of frequency of collection on sperm density and on 



concentration of fructose and lactic acid in fresh bull semen 



(Mann, 1948a) 



Pre-sperm, sperm-containing, and post-sperm fractions in the ejaculate 

 To assess correctly the composition of individual specimens of 

 semen it is essential to bear in mind the fact that in some species 

 (e.g. man, boar, stallion) the different portions of semen follow 

 one another in a definite order of sequence. This has been demon- 

 strated by the so-called split-ejaculate method which depends on the 

 collection and analysis of separate fractions of the same ejaculate 

 according to the time of delivery from the urethra. In man, the 

 ejaculation is initiated by the secretion of Cowper's glands, the pros- 

 tatic secretion is delivered next, to be followed by the sperm and the 

 vesicular secretion (Broesike, 1912; Huggins and Johnson, 1933; 

 MacLeod and Hotchkiss, 1942; Lundquist, 19496; Pryde, 1950); 

 according to Lundquist, in man the prostatic secretion contributes 

 from 13 to 32% and the vesicular secretion from 46 to 80% of the 

 whole ejaculate. 



In the boar, an animal with a protracted period of ejaculation, 

 the semen consists of two portions, gel and liquid. McKenzie et al. 

 (1938) calculated that 15-20% of the liquid portion is derived from 

 the seminal vesicles, 2-5% from the epididymis, 10-25% from 

 Cowper's gland, and the rest is made up by the urethral glands 

 secretion. We have made a similar investigation (Mann and Glover, 

 1954) using estimations of sperm concentration in ejaculated and 

 epididymal semen for the assessment of the epididymal contribution, 

 and the chemical determinations of fructose, citric acid and ergo- 

 thioneine in the ejaculated semen and in the vesicular secretion as 

 4 



