AND NERVOUS SYSTEMS. 229 



" 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 car- 

 ries the influence of the will towards the muscle, which 

 nerve has no power to convey an impression backwards 

 to the brain ; and that another nerve connects the mus- 

 cle with the brain, and, acting as a sentient nerve, con- 

 veys the impression of the condition of the muscle to 

 the mind, but has no operation in a direction outwards 

 from the brain towards the muscle, and does not there- 

 fore excite the muscle however irritated." 



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. 



The same process takes place in every action which 

 we perform. When we direct our eyes towards a 

 landscape, for instance, and having examined one group 

 of objects, move them ever so little towards 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 upwards, or 

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