MUSCULAR AND NERVOUS SYSTEMS. 225 



705. " I find that to the full operation of the muscular 

 power, two distinct filaments of nerves are necessary, and 

 that a circle is established between the sensorium and the 

 muscle ; that one filament or single nerve carries the in- 

 fluence of the will toward the muscle, which nerve has 

 no power to convey an impression backward to the 

 brain ; and that another nerve connects the muscle with 

 the brain, and, acting as a sentient-nerve, conveys the 

 impression of the condition of the muscle to the mind, but 

 has no operation in a direction outward from the brain 

 toward the muscle, and does not therefore excite the mus- 

 cle, however irritated." 



706. Thus we are, it would seem, furnished with a 

 double apparatus, by means of distinct nervous filaments, 

 one for muscular action and the other for sensation, the 

 one to carry our commands from the brain to any mus- 

 cle which we would* have contract, and the other to 

 bring back an account of the condition of said muscle, 

 and inform us whether the contraction is too great or 

 too little, or whether the direction of the lever which 

 the muscle has been concerned in moving is precisely 

 such as to answer the purpose intended. Thus as the 

 painter goes on with his work, these sentient-nerves con- 

 stantly warn him precisely how much muscular move- 

 ment is required in his hand to place his colors according 

 to his taste; while the nerves of contraction move the 

 muscles exactly as the will directs them, and as these 

 different kinds of information are conveyed from and to 

 the brain in an instant, or " as quick as thought," so we 

 are insensible of the lapse of the least portion of time 

 between the mandate from the brain and the action of the 

 muscles. 



707. The same process takes place in every action which 

 we perform. When we direct our eyes toward a land- 

 scape, for instance, and having examined one group of 

 objects, move them ever so little toward the next, this 

 is not done without the action of the sentient-nerves, 

 which inform the brain exactly of the situation of the 

 muscles of the eyes; which muscles, in their turn, are 

 directed how to move the orbits. Thus, if we wish to 

 turn the eye from right to left, or upward, or down- 



