REFLEX FUNCTION OF THE SPINAL CORD. 507 



act governed by the spinal cord : the irritation of the glans 

 penis conducted to the spinal cord, and thence reflected, 

 excites the successive and co-ordinate contractions of the 

 muscular fibres of the vasa deferentia and vesiculee semi- 

 nales, and of the accelerator urinee and other muscles of 

 the urethra ; and a forcible expulsion of semen takes place, 

 over which the mind has little or no control, and which, in 

 cases of paraplegia, may be unfelt. The erection of the 

 penis also, as already explained (p. 196), appears to be in 

 part the result of a reflex contraction of the muscles by 

 which the veins returning the blood from the penis are 

 compressed. Irritation of the vagina in sexual intercourse 

 appears also to be propagated to the spinal cord, and thence 

 reflected to the motor nerves supplying the Fallopian tubes. 

 The involuntary action of the uterus in expelling its con- 

 tents during parturition, is also of a purely reflex kind, 

 dependent in part upon the spinal cord, though in part 

 also upon the sympathetic system ; its independence of the 

 brain being proved by cases of delivery in paraplegic 

 women, and now more abundantly shown in the use of 

 chloroform. 



Besides these acts regularly performed under the influ- 

 ence of the reflecting power of the spinal cord, others are 

 manifested in accidents ; such as the movement of the limbs 

 and other parts to guard the body against the effects of 

 sudden danger. When, for example, a limb is pricked or 

 struck, it is instantly and involuntarily withdrawn from the 

 instrument of injury; and the same preservative tendency 

 of the reflex power of the cord is shown in the outstretched 

 arms when falling forwards, and their reversed position 

 when falling backwards ; the action, although apparently 

 voluntary, being really, in most cases, only an instance of 

 reflex action. 



To these instances of spinal reflex action, some add yet 

 many more, including nearly all the acts which seem to be 

 performed unconsciously, such as those of walking, running, 

 writing, and the like : for these are really involuntary 



