898 THE PHYSIOLOGY OF REPRODUCTION. 



some part of the genital tract, from the testes themselves, from 

 the urethra or prostate gland, and especially from the glans penis. 

 Mechanical stimulation of the glans leads to erection, and Eckhard 

 showed in dogs that section of the pudic nerve prevents this reflex 

 from occurring, proving, therefore, that the sensory fibers concerned 

 run in the pudic nerve. Stimulation of these latter fibers leads also 

 to erotic sensations and eventually to the completion of the sexual 

 orgasm. This latter act brings about the forcible ejection of the 

 sperm through the urethra. It is initiated by contractions of the 

 musculature of the vasa deferentia, ejaculatory duct, the seminal 

 vesicles, and the prostate gland, which force the spermatozoa, to- 

 gether with the secretions of the vesicles and prostate gland, into 

 the urethra, whence they are expelled in the culminating stage of 

 the orgasm by the rhythmical contractions of the ischiocavernosus 

 and bulbocavernosus muscles, together with the constrictor urethrae. 

 The immediate center for this complex reflex is assumed to lie in 

 the lumbar cord, since, according to the experiments of Goltz, 

 mechanical stimulation of the glans in dogs causes erection and 

 seminal emission after the lumbar cord is severed from the rest of 

 the central nervous system. Under ordinary conditions the act is 

 accompanied by strong psychical reactions which indicate that 

 the cortical region of the cerebrum is involved. It is interesting in 

 this connection to find that electrical stimulation of a definite re- 

 gion in the cortex* of dogs may cause erection and ejaculation. 



* Pussep, quoted from Hermann's " Jahresbericht der Physiologic," 

 vol. xi, 1903. 



