IMPREGNATION 



439 



by no means certain. The secretion of the prostate seems to preserve 

 the vitality of the spermatozoa, while that of Cowper's gland is a mucus 

 which prevents their too wide dissipation in the vagina. 



The amount of semen deposited in the fornix at each coitus depends 

 on the vigor of the sexuality of the male and on the time since ejaculation 

 previously occurred. In normal cases, that is when coitus does not 

 take place oftener than six or seven times per month, the average amount 

 is 3 or 4 c.c., but it may be much larger at a single emission and much 

 more abundantly produced. In old men semen is produced many years 

 after the power of erection and intromission has gone. The sperma- 

 tozoa are easily killed by the Rontgen rays, etc., and in some cases 

 spermatogenesis appears to stop, at least for many months. In young 

 men it is apparently the distention of the seminiferous tubules with the 



FIG. 251 



Section through the round ligament of the human uterus. (Kolliker.) On the ieft are many 

 bundles of cross-striated muscle-fibers, and on the right is the smooth musculature. In the 

 center are vessels. Thus we see that the movements of the uterus (as in coitus, etc.) may) be 

 under many sorts of influence perhaps voluntary as well as reflex. 



constantly secreted sperms, etc., which raises the irritability of the sexual 

 nerve-centers and thus leads to sexual desire; in the woman these condi- 

 tions are largely lacking, for no such pressure can arise. Under the influ- 

 ence of erotic impressions, nervous or imaginary, the semen is rapidly 

 secreted and this distention may become almost painful. There is some 

 evidence that semen contains some substance (enzyme?) that when 

 absorbed into the circulation stimulates metabolic vigor. This action 

 is apparently often to be seen in the physical improvement of newly 

 married women. 



Fertilization in the more technical sense is the union of the spermatozoa 

 with the ovum. This leads to the development of the latter into a 

 new individual possessing the characters of both parents. In a broader 

 sense it is the woman that is fertilized not by the union of the sexual' 



