506 THE NERVOUS SYSTEM. 



movements may be performed while the mind is, in other 

 things, fully occupied, 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, etc. 

 Being, for ordinary purposes, independent of the will and 

 consciousness, they are performed perfectly, without expe- 

 rience 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 continuance 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 

 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 



