184 The Biochemistry of Semen 



a reaction described in 1897 by another Swedisli investigator, 



Stahre. 



CH2COOH 



I 

 C(OH)COOH 



i 

 CH2COOH 



Citric acid 



Schersten enlarged his original finding by noting that citric acid 

 in semen is derived from the male accessory organs of reproduction; 

 in man, from the prostatic secretion, in the boar and bull, from the 

 vesicular secretion. His findings have since been confirmed and 

 extended by several investigators. In nine samples of human pros- 

 tatic secretion Huggins and Neal (1942) recorded values ranging 

 from 480 to 2688 mg. citric acid /1 00 ml., while two analyses of 

 human seminal vesicle secretion gave 15 and 22 mg./lOO ml; in fif- 

 teen specimens of human semen, the values ranged from 140 to 

 637 mg./lOO ml. A survey by Harvey (1951), which covered 725 

 specimens of human semen from 371 donors, revealed contents 

 ranging from to 2340 mg./lOO ml.; the mean value of citric acid 

 for the whole group was 479 mg./lOO ml. and 12-6 mg. /ejaculate. 

 Citric acid also occurs normally in the semen of other mammalian 

 species; a high concentration is characteristic for the bull (510- 

 1100 mg./lOO ml.), boar (130 mg./lOO ml.), ram (110-260 mg./lOO 

 ml.), and rabbit (110-550 mg./lOO ml.); rather lower concentrations 

 are found in stallions (Humphrey and Mann, 1948, 1949). In some 

 animals, e.g. the bull, ram, boar, and stallion, citric acid originates 

 in the seminal vesicle, the same organ which also secretes fructose. 

 In other species, however, the two substances are secreted in dif- 

 ferent parts of the male reproductive system (Table 24). In the 

 rabbit citric acid is limited largely to the gel-portion of semen, and it 

 is produced by the glandula vesicularis, whereas fructose, it will be 

 remembered, is secreted also in the prostate. An even clearer separa- 

 tion occurs in the rat where fructose is found in the coagulating 

 glands and in the dorso-lateral prostate, whereas citric acid is 

 produced by the ventral prostate and the lateral lobes of the dorso- 

 lateral prostate (Fig. 4). It is however, probable that even in species 

 such as the bull, where citric acid and fructose are found side by 



