138 The Biochemistry of Semen 



level of the ejaculatory ducts will prevent both fructose and sperma- 

 tozoa from reaching the urethral canal. This fact has been aptly 

 chosen as an aid to medical diagnosis by Young (1948, 1949) 

 who described the case of a man in whom repeated semen analysis 

 failed to detect fructose or sperm, although testicular biopsy re- 

 vealed normal spermatogenesis; the case has been diagnosed as 

 congenital bilateral aplasia of the vasa deferentia. 



It must be also mentioned that though the seminal vesicles are 

 the main source of fructose in the higher mammals, yet an addi- 

 tional small amount of this seminal sugar is derived from the 

 ampullar glands (Mann, 1948^), and in some animals also from 

 certain other glands. Thus, in the rabbit, fructose was located both 

 in the glandula vesicularis (a structure corresponding to seminal 

 vesicles) and in the ampullae, as well as in the prostate (Davies and 

 Mann, \9Alb). The rat provides an instance of particular interest, 

 as in this rodent the seminal vesicles are free from fructose alto- 

 gether; instead, fructose is found in the dorso-lateral prostate and 

 in the so-called coagulating gland, a small organ immediately 

 adjacent to the seminal vesicles proper, with which it shares a 

 common peritoneal sheath (Humphrey and Mann, 1948, 1949). 



Since fructose is produced by the accessory glands, and not the 

 testes, it is not surprising that in whole fresh semen there is no 

 direct proportion between fructose concentration and sperm density. 

 On the contrary, both in man and in domestic animals, an inverse 

 ratio between fructose and sperm concentration in semen is fre- 

 quently met with; the simplest interpretation is that in a dense 

 sample of semen the space occupied by the sperm cells is relatively 

 larger, and the volume taken up by the fluid portion, i.e. the 

 fructose-containing seminal plasma, correspondingly less. This 

 factor has a direct bearing on the interpretation of laboratory 

 examinations concerned with semen and male fertility or sterility. 

 It explains, for instance, why a semen sample with a high content 

 of fructose need not necessarily be one of good sperm quality, and 

 furthermore, why it is possible to come across samples with a high 

 fructose content but of low sperm density. In fact, some of our 

 highest values for fructose so far recorded, were encountered in 

 the semen of vasectomized, and thus completely azoospermic, 

 individuals. 



