694 REPRODUCTION AND GROWTH 



studied later by Loven and others, leave the spinal cord in the anterior roots 

 of the first to third sacral nerves, unite with the hypogastric plexus and run 

 thence to the penis. They have their center in the lowermost part of the 

 cord, so that erection can still be reflexly induced after section of the spinal 

 cord between the dorsal and the lumbar regions (cf. page 588). In fact, at 

 the moment of making such a section (in the guinea pig) erection and ejacu- 

 lation occur (Spina). 



According to L. R. Miiller erection and ejaculation can be induced (in the 

 dog) by rubbing 1 the penis after extirpation of the lumbar and upper part of 

 the sacral cord. It is likely therefore that the reflex can be mediated by periph- 

 eral ganglion 'cells. 



Erection may be brought about also through the influence of higher nerve 

 centers. Eckhard was able to induce the phenomenon in animals by the elec- 

 trical stimulation of the cervical cord, of the pons, and of the crura cerebri. 

 The fact that in man erection often occurs merely as the result of erotic 

 ideas, is evidence that the nervi erigentes may be excited in the same way 

 also by the cerebrum. 



Stimulation of the nervi erigentes increases the volume of blood flowing 

 through the pudenda interna vein beyond the mouth of the penis vein to about 

 eightfold the volume flowing during the relaxed condition of the penis. Since, 

 however, erection occurs as the result of the same stimulation the inflow of 

 blood must be still greater. In erection as it occurs naturally the veins of the 

 penis are compressed by contraction of the musculature about the urethra, 

 thereby rendering the outflow of blood from the penis more difficult, which in 

 turn serves to heighten the degree of erection. Compression of these veins 

 alone however does not cause erection. 



Erection obviously must be closely related to the functions of the testes; 

 and yet observations on both men and animals go to show that erection is pos- 

 sible after castration and that sexual passion may not be entirely destroyed. 



When ejaculation occurs, the seminal fluid is thrown by forcible contrac- 

 tions of the vasa deferentia into the urethra in the direction of the pars mem- 

 branacea urethra?. Entrance to the urinary bladder is prevented chiefly by the 

 sphincter of the bladder and by contraction of the musculature of the prostate. 



The ejaculatory ducts open at the summit of the seminal eminence, while 

 the mouths of the numerous ducts, from the prostate are so arranged that they 

 empty their secretion in exactly the opposite direction. When the semen pours 

 out of the ejaculatory ducts, numerous streams of the secretion from the pros- 

 tate are at the same time poured into the urethra and there results a very 

 uniform mixture of the two fluids (Walker). 



The seminal fluid is expelled from the urethra by contraction of the bulbo- 

 cavernosus and the ischio-cavernosus muscles ; according to Walker the sphincter 

 urethrse membranacese should play an essential part in this also. 



Ejaculation may take place without erection in the guinea pig, for example, 

 when the spinal cord is crushed by means of an exploring instrument. In the 

 same animal Remy found on the inferior vena cava at the level of the renal 

 veins a small ganglion electrical stimulation of which produced a sudden ejacu- 

 lation. Sexual desire was not destroyed by section of the nerves issuing from 

 this ganglion, but erection and ejaculation were no longer possible. 



