REFLEX FUNCTION OF THE SPINAL CORD. 399 



or in sleep powerless; yet in an emergency, the mind can 

 direct and strengthen them : and it can adapt them to the 

 several acts of speech, effort, &c. Being, for ordinary par- 

 poses, independent of the will and consciousness, they are per- 

 formed perfectly, without experience or education of the mind ; 

 yet they may be employed for other and extraordinary uses 

 when the mind wills, and so far as it acquires power over them. 

 Being commonly independent of the brain, their constant con- 

 tinuance does not produce weariness ; for it is only in the brain 

 that it or any other sensation can be perceived. 



The subjection of the muscles to both the spinal cord and 

 the brain, makes it difficult to determine in man what move- 

 ments or what share in any of them can be assigned to the re- 

 flecting power of the cord. The fact that after division or 

 disorganization of a part of the cord, movements, and even 

 forcible though purposeless ones, are produced 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 perfect, it may supply the 

 nervous stimulus, and the will the direction. As instances in 

 which it supplies both stimulus and direction, that is, both ex- 

 cites and determines the combination of muscles, may be men- 

 tioned the acts of the abdominal 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 postponing or modifying the act, there are all 

 the evidences of reflex action ; namely, the necessary prece- 

 dence of a stimulus, the independence of the will, and, some- 

 times, of consciousness, the combination of many muscles, the 

 perfection 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, ex- 

 cites the successive and co-ordinate contractions of the muscu- 

 lar fibres of the vasa deferentia and vesiculse seminales, and of 

 the accelerator urinse 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 ex- 

 plained (p. 153), 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 



