38 The Biochemistry of Semen 



origin. Within a few minutes, that is followed by a sperm-containing 

 fraction which may also contain some gel-like material. As a rule 

 however, the gel forms a distinct fraction and is voided shortly after 

 the sperm fraction. Moreover, these three fractions, which complete 

 an ejaculation 'wave', may be succeeded by a second 'wave', also 

 fractionated. The two waves together may last up to 30 min., and 

 represent in fact, two successive ejaculates. By the estimation of 

 sperm concentration coupled with the chemical determination of 

 fructose, citric acid, and ergothioneine in the various fractions, it is 

 possible to show that during the ejaculation the seminal vesicle 

 secretion follows immediately upon the delivery of the spermatozoa, 

 and is found mainly in the sperm-containing fraction (Glover and 

 Mann, 1954; Fig. 7). Occasionally, however, the ejaculation of 

 semen is incomplete and the semen does not include the later 

 fractions. When this happens, for example in the stallion, certain 

 normal constituents such as fructose or citric acid, may be missing 

 altogether. Obviously, such incomplete ejaculations create a further 

 complication in the assessment of analytical results obtained with 

 semen, at any rate in those species in which the ejaculation is a 

 fractionated one. But even in the bull where under physiological 

 conditions ejaculation appears to be instantaneous, the 'split- 

 ejaculate method' applied by Lutwak-Mann and Rowson (1953) 

 with the aid of electric stimulation, demonstrated the occurrence in 

 electrically-induced ejaculates, of at least two distinct fractions; of 

 these, the first was a copious sperm-free fraction, slightly viscous, 

 colourless, and of urethral origin, in which there was no fructose or 

 citric acid and very little protein; the next was a creamy sperm- 

 containing fraction, followed by, or more often mixed with, a yel- 

 lowish-coloured post-sperm fraction which represented an almost 

 pure secretion of the seminal vesicles, with a characteristically high 

 content of fructose, citric acid, and 5-nucleotidase. 



Criteria for the rating of semen quality 



General medical and veterinary experience indicates that the suc- 

 cessful fertihzation of the ovum and initiation of pregnancy, while 

 it is brought about primarily by the spermatozoa present in an 

 ejaculate, demands nevertheless the attainment of certain qualita- 

 tive and quantitative standards by the semen. We should therefore, 



