J 826.] Philosophical Transact ions for 1826, Parts L and 11,229 



of the muscle, we have next to show that a motor nerve is not 

 a conductor towards the brain, and that it cannot perform the 

 office of a sensitive nerve. 



'' Without attempting to determine the cause, whether 

 depending on the structure of the nervous cord, or the nature, 

 or the source of the fluid contained, a pure or simple nerve has 

 the influence propagated along it in one direction only, and not 

 backwards and forwards ; it has no reflected operation or power 

 retrograde ; it does not both act from and to the sensorium. 



'* Indeed reason without experience would lead us to conclude, 

 that whatever may be the state, or the nature of the activity of 

 a motor nerve during exertion, it supposes an energy proceeding 

 from the brain towards the muscles, and precludes the activity 

 of the same nerve in the opposite direction at the same moment. 

 It does not seem possible therefore that a motor nerve can be 

 the means of communicating the condition of the muscles to the 

 brain. 



" Expose the two nerves of a muscle ; irritate one of them, 

 and the muscle will act ; irritate the other, and the muscle 

 remains at rest. Cut across the nerve which had the power of 

 exciting the muscle, and stimulate the one which is undivided 

 — the animal will give indication of pain; but although the 

 nerve be injured so as to cause universal agitation, the muscle 

 with which it is directly connected does not move. Both nerves 

 being cut across, we shall still find that by exciting one nerve 

 the muscle is made to act, even days after the nerve has been 

 divided ; but the other nerve has no influence at all. 



*' Anatomy forbids us to hope that the experiment will be as 

 decisive when we apply the irritants to the extremities of the 

 divided nerves which are connected with the brain ; for all the 

 muscular nerves receive more or less minute filaments of sensi- 

 tive nerves, and these we can trace into them by the knife, and 

 consequently, they will indicate a certain degree of sensibility 

 when hurt. To expose these nerves near their origins, and 

 before any filament of a sensitive nerve mingles with them, 

 requires the operator to cut deep, to break up the bones, and to 

 divide the blood-vessels. All such experiments are much better 

 omitted ; they never can lead to satisfactory conclusions." 



^ ^ ^ ^ '^ 



" Between the brain and the muscles there is a circle of nerves ; 

 one nerve conveys the influence from the brain to the muscle, 

 another gives the sense of the condition of the muscle to the brain. 

 If the circle be broken by the division of the motor nerve, 

 motion ceases ; if it be broken by the division of the other 

 nerve, there is no longer a sense of the condition of the muscle, 

 and therefore no regulation of its activity.*' 



*'* Thus led to conclude that there is motion in a circle, we nevertheless cannot 

 adopt the hypothesis of circulating fluids. That a fluid does not proceed from the brain, 



