BEFLEX FUNCTION OF THE SPINAL COED. 505 



and the brain, makes it difficult to determine in man what 

 movements or what share in any of them can be assigned 

 to the reflecting power of the cord. The fact that after 

 division or disorganization of a part of the cord, move- 

 ments, and even forcible though purposeless ones, are pro- 

 duced in the lower limbs when the skin is irritated, proves 

 that the spinal cord can reflect a stimulus to the action of 

 the muscles that are, naturally, most under the control of 

 the will ; and it is, therefore, not improbable that, for even 

 the involuntary action of those muscles, when the cord is per- 

 fect, it may supply the nervous stimulus, and the will the 

 direction. As instances in which it supplies both stimulus 

 and direction, that is, both excites and determines the com- 

 bination of muscles, may be mentioned the acts of the abdo- 

 minal muscles in vomiting and voiding the contents of the 

 bladder and rectum ; in both of which, though, after the 

 period of infancy, the mind may have the power of post- 

 poning or modifying the act, there are all the evidences of 

 reflex action; namely, the necessary precedence of a sti- 

 mulus, the independence of the will, and, sometimes of 

 consciousness, the combination of many muscles, the per- 

 fection of the act without the help of education or experi- 

 ence, and its failure or imperfection in disease of the lower 

 part of the cord. The emission of semen is equally a reflex 

 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 vesiculse semi- 

 nales, and of the accelerator urinae 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. 185), 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 



