176 THE PHYSIOLOGY OF REPRODUCTION 



phenomena which, according to their view, are usually associated 

 with the male sex. 



Seminal Fluid 



The semen serves as the mechanical medium in which the 

 spermatozoa move. It is possible also that it has a nutritive 

 function. It is secreted by the seminiferous tubules. It is milky 

 in appearance, and has a characteristic smell. When ejected the 

 seminal fluid is mixed with the secretions of the accessory 

 glands (prostate, &c.), which render it still more milky. On 

 standing it tends to become gelatinous. According to Lode,* 

 the specific gravity of semen is between 1'027 and 1-046. 



The number of spermatozoa which exist in normal human 

 semen is subject to much variation. Lode ^ has shown that it 

 diminishes almost to zero after a number of successive emissions, 

 but increases again after an interval of several days. The average 

 number is given as 60,000 per cubic centimetre. The number 

 of sperms present in the ejected seminal fluid of the dog was 

 also found to be greater at the end of an interval in which there 

 were no emissions, but it did not continue to increase after more 

 than eight or ten days. In a normal emission of semen (Man) 

 Lode calculates that there are about 226,000,000 spermatozoa, 

 but that the number may vary from zero to 551,000,000. 



The spermatozoa which are not ejaculated degenerate. 

 The tails break off, and undergo a gradual Kquef action. The 

 end products are ultimately absorbed by the epithelial cells of 

 the seminal vesicles, and perhaps by the cells of the vasa de- 

 ferentia or of the testis itself. According to Perez, ^ the sperma- 

 tozoa of male newts which are kept apart from females are 

 absorbed by phagocytes.* 



Movements of Spebmatozoa 

 When the spermatozoa are in the testis they are inactive, but 

 they begin to move rapidly as soon as they are* ejected in the 



1 Lode, "UntersuohuDgen iiber die Zahlen- und Regenerationsverhaltnisse 

 der Spermatozoiden bei Hund und Mensoh," Pfiiigers Arch., vol. 1., 1891. 



^ Lode calculates that about 339,385,500,000 spermatozoa must be pro- 

 duced in man between the ages of twenty-five and fifty-five. 



' Perez, " Resorption phagocytaire des Spermatozoides," Proces- Veriaux 

 de la Soc. das Sciences de Bordeaux, 1904. 



J The chemistry of the spermatozoon and semen is dealt with in 

 Chapter VIII. 



