136 The Biochemistry of Semen 



crystalline compound which has been shown by Neuberg (Neuberg, 

 1902, 1904; Neuberg and Strauss, 1902; Langstein and Neuberg, 

 1907; Neuberg and Mandl, 1946) to be one of the few chemical 

 derivatives by means of which fructose can be identified and dis- 

 tinguished from glucose and from other closely related sugars; {b) the 

 purification of seminal fructose up to the point when it reached the 

 specific optical activity of pure crystalline fructose: [aP°°= -92-2°; 

 (c) the demonstration that fructose occurs in the semen in free form 

 and that it accounts for the whole of the yeast-fermentable carbo- 

 hydrate which yields 'ketose reactions' with resorcinol (Seliwanoff, 

 1887; Roe, 1934), diphenylamine (Ihl, 1885) and similar colour- 

 producing substances (Pinoff, 1905; Thomas and Maftei, 1927; 

 Pryde, 1946); {d) proof obtained with the highly specific enzyme, 

 glucose oxidase, that in semen glucose is either absent or present in 

 mere traces. 



On the basis of the above findings, which excluded the presence 

 of glucose, bound fructose, and other ketoses, a rapid colorimetric 

 method has been developed by means of which it is possible to 

 determine accurately the fructose content of semen; 05-0 1 ml. 

 suffices for analysis of human, bull, ram or rabbit semen (Mann, 

 1948a, b\ 1952). 



Species differences 



The following mammalian species have been found to contain 

 fructose in semen: man, bull, ram, boar, stallion, goat, opossum, 

 rabbit, guinea-pig, rat, mouse, hamster (Mann, 1949). Among the 

 lower animals, fructose was found in the semen of an elasmobranch 

 (the dogfish, Scylliorhinus caniculus) and in the reproductive organs 

 of the male (but not female) grasshopper, Locusta migratoria 

 (Humphrey and Mann, 1948; Humphrey, 1949). In this connection 

 it is worthwhile to recall the occurrence of fructose in the haemo- 

 lymph of the larvae of another insect, Gastrophiliis intestinalis 

 (Levenbook, 1947). 



There are, however, considerable quantitative differences between 

 the various species. In the bull and goat, for example, the con- 

 centration of fructose in semen sometimes reaches a level of 

 1000 mg./lOO ml., but in the boar and stallion it seldom exceeds 

 50 mg./lOO ml. Human semen occupies an intermediate position as 



