398 THE NERVOUS SYSTEM. 



animals can perform, are also always, in the entire and healthy 

 state, performed involuntarily, and under the sole influence of 

 the cord ; but it is probable that such acts may be, and com- 

 monly are, so performed, the higher nerve-centres of the ani- 

 mal having only the same kind of influence in modifying and 

 directing them, that those of man have in modifying and di- 

 recting the movements of the respiratory muscles. 



The fact that such movements as are produced by irritating 

 the skin of the lower extremities in the human subject, after 

 division or disorganization of a part of the spinal cord, do not 

 follow the same irritation when the mind is active and con- 

 nected with the cord through the brain, is, probably, due to 

 the mind ordinarily perceiving the irritation and instantly 

 controlling the muscles of the irritated and other parts ; for, 

 even when the cord is perfect, such involuntary movements 

 will often follow irritation, if it be applied when the mind is 

 wholly occupied. When, for example, one is anxiously think- 

 ing, even slight stimuli will produce involuntary and reflex 

 movements. So, also, during sleep, such reflex movements 

 may be observed when the skin is touched or tickled; for ex- 

 ample, when one touches with the finger the palm of the hand 

 of a sleeping child, the finger is grasped the impression on 

 the skin of the palm producing a reflex movement of the 

 muscles which close the hand. But when the child is awake, 

 no such effect is produced by a similar touch. 



On the whole, it may, from these and like facts, be concluded 

 that the proper reflex acts, performed under the influence of 

 the reflecting power of the spinal cord, are essentially inde- 

 pendent of the brain, and may be performed perfectly when 

 the brain is separated from the cord : l that these include a 

 much larger number of the natural and purposive movements 

 of the lower animals than of the warm-blooded animals and 

 man : and that over nearly all of them the mind may exer- 

 cise, through the brain, some control ; determining, directing, 

 hindering, or modifying them, either by direct action or by its 

 power over associated muscles. 



In this fact, that the reflex movements from the cord may 

 be perfectly performed without the intervention of conscious- 

 ness or will, yet are amenable to the control of the will, we 

 may see their admirable adaptation to the well-being of the 

 body. Thus, for example, the respiratory movements may be 

 performed while the mind is, in other things, fully occupied, 



1 Reflex movements, occurring quite independently of sensation, 

 are generally called exclto-motor ; those which are guided or accom- 

 panied by sensation, but not to the extent of a distinct perception or 

 intellectual process, are termed sensor i-motor. 



