The Influence of Extraneous Factors 67 



through the optic nerves, are probably responsible for the changes 

 associated with the so-called male sex cycle; many lower vertebrates 

 produce spermatozoa only during a brief period, once a year, and 

 even among mammals, there are many species in which male sexual 

 activity is restricted to definite season. Sperm survival in the epidi- 

 dymis and sperm transport in the female reproductive tract, are also 

 two phenomena which probably depend on pituitary function; the 

 former on the normal gonadotrophic activity of the anterior lobe, 

 the latter on impulses transmitted to the uterus by the oxytocic 

 hormone secreted in the posterior lobe. 



The function of testicular hormone, in so far as semen is con- 

 cerned, is to provide the stimulus necessary for the elaboration of 

 seminal plasma and for ejaculation. The male sex hormone is 

 intrinsically linked with the production of seminal plasma by the 

 accessory organs; it regulates the secretory activity of the accessory 

 organs, and thus determines not only the output of the seminal 

 plasma as a whole, but also the relative contribution of each indi- 

 vidual gland towards the ultimate make-up of semen. 



The earlier morphological studies have provided much funda- 

 mental information which has helped to build up our knowledge of 

 the relationship between the functional state of the male accessory 

 organs and androgenic activity. These investigations have shown 

 that postcastrate retrogressive changes in the gross appearance and 

 in the microscopic structure of the accessory organs can be pre- 

 vented, or reversed, by the administration of testicular hormone. On 

 this basis several so-called 'hormone indicator tests' have been 

 elaborated for the detection of male sex hormone activity (cf. Moore, 

 1937; Price, 1947; Dorfman, 1950). Two such tests also involved 

 semen examination: the so-called 'clotting test' was based on the 

 observation that the formation of a clot in the electrically-induced 

 seminal discharge of a guinea-pig depends on the presence of male 

 sex hormone, and the 'spermatozoon motility test' was derived 

 from the observation that in the epididymis severed from the testis, 

 spermatozoa survive longer if the testis is not removed from the 

 body; presumably, the testicular hormone is capable of stimulating 

 the epididymal cells to secrete some substance necessary for the 

 preservation of epididymal spermatozoa (Moore, 1935; Parsons, 

 1950). 

 6 



