CONCLUDING REMARKS 



A STRIKING feature of semen which did not escape Leeuwenhoek, 

 and which has been abundantly and repeatedly confirmed since, is 

 the extraordinary diversity of shape and structure, encountered 

 among the spermatozoa of different species. It even led Wagner and 

 Leuckart (1852) to state 'that one may often safely venture to infer 

 from the specific shape of these elements the systematic position 

 and the name of the animals investigated'. Similarly, anatomists and 

 physiologists aUke, have long accepted as natural the existence of 

 remarkable species variations in the form and size of the male 

 accessory glands, the organs responsible for the elaboration of that 

 apparently indispensable adjunct of spermatozoa, the seminal 

 plasma. It behoves us, I feel, to adopt a similarly enlightened atti- 

 tude of mind towards the chemistry of semen. Is it not rather un- 

 reasonable to expect that chemical findings made with the semen of 

 one species must needs extend to that of others? The fact that a 

 given substance is found in substantial amounts in the semen of one 

 species, but is missing in others, by no means detracts from its 

 physiological value: on the contrary, it is highly probable that such 

 species-restricted occurrence is intimately linked with some other 

 biological characteristics, peculiar to certain, but not necessarily 

 all, animal species. 



A critical approach, free from bias, is also called for in the 

 comparative evaluation of the morphological and chemical findings 

 in semen. To expect, as has been done, the existence of a strict cor- 

 relation between say, the fructose level in seminal plasma and sperm 

 density in semen, is no more justifiable than to look for a relation- 

 ship between, for instance, the glucose level in blood plasma and 

 the number of red cells in blood. Similarly, although the secretion 

 of fructose in the accessory organs depends closely upon the activity 

 of the male sex hormone, it would be mistaken to attribute the level 

 of fructose in semen to the influence of this hormone alone, because 

 in reality it is conditioned by a multitude of other factors, including 

 the general nutritional state of the body, size and storage capacity 



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