Fructose and Fructolysis 1 59 



spermatozoa, both depend on the maintenance of the normal 

 metaboHsm of fructose. 



We still remain confronted with two questions to which, it is 

 confidently hoped, further research will bring answers. One involves 

 the as yet obscure position in the semen of animal species which lack 

 fructose. Secondly, one wonders why nature should have chosen 

 fructose and not glucose, as the natural substrate for sperm meta- 

 bolism. At this point, conditions in another body fluid, the milk, 

 come to mind; there, the occurrence of lactose poses a somewhat 

 similar question. But in considering the matter, several facts must 

 be taken into account. To begin with, if glucose and not fructose 

 were present in semen, its concentration could hardly be expected 

 to exceed that of blood and other body fluids. Thus, it might not 

 be sufficient to satisfy the metabolic requirements of spermatozoa 

 which, unlike most other animal cells, are capable of utilizing fruc- 

 tose anaerobically; it is worth noting that on the whole, yeasts and 

 bacteria are also unable to consume fructose at the same rate as 

 glucose. Presumably, this enables the spermatozoa to draw freely 

 upon seminal fructose without, as it were, competition from other 

 tissues. Lastly, the intimate relationship between seminal fructose 

 and the male sex hormone must not be lost sight of; it would be 

 rather difficult to envisage a similar dependence in the case of 

 glucose, bearing in mind the ubiquitous occurrence and physio- 

 logical function of this sugar. 



