168 report — 1859. 



animal, that is to say, whether the brain may not be the source of the phenomena ? 

 To settle this, the author repeated the experiments on frogs without their brains, and 

 without their skins. The phenomena were precisely as before. 



Experiment having thus proved that the sensations assigned to the muscular sense 

 have not their source in the skin nor in the brain, the only alternative is to con- 

 clude that their source is the muscles themselves, the action of which awakens the 

 sensibility of the spinal cord, either through the anterior, or through the posterior 

 root of the spinal nerves — in the author's belief, it is through the anterior root. 



On the stijiposed Distinction between Sensory and Motory Nerves. 

 By G. H. Lewes. 



The author began by declaring the anatomical discovery of Sir Charles Bell to be 

 firmly fixed ; but the physiological inference deduced from it to be questionable. The 

 fact that the anterior roots supplied the nerves to the muscles, and the posterior 

 roots supplied those to the surfaces, established an anatomical difference between 

 muscle-nerves and skin- nerves, but did not establish the physiological inference that 

 muscle-nerves were only motory, and skin-nerves only sensory. The author held 

 that both nerves were sensory and motory ; but that owing to their anatomical con- 

 nexions, the anterior nerves were more largely implicated in motions, and the poste- 

 rior in sensations. 



The supposed distinction between the two classes, if essential, and not merely one 

 of degree, must be either a distinction in property or in function. That there was 

 no essential distinction in properly, seemed proved by their identity of structure. This 

 the author showed in detail. Then, as to the distinction in function, it was easy to 

 see this could only be one of degree, since function is determined by anatomical con- 

 nexions ; and these are much more alike than is generally supposed. 



There are nerves which on being irritated excite muscular contractions ; and these 

 nerves we can follow into the very substance of the muscles, where they end. There 

 are other nerves which on being irritated excite sensations ; and these we can follow 

 iuto the substance of the sensitive surfaces, where they end. Finally, there are 

 nerves which excite both contractions and sensations, and these we can follow into 

 muscles and the skin. This is Bell's immortal discovery. This is the anatomical 

 distribution of the nerves. Yet it does not force assent to the proposition that one 

 of these nerves is sensory and the other motory, because in the foregoing we have 

 only described one half of the anatomical distribution of the nerves. Let the whole 

 description be given as modern investigations enable us to give it, and there will no 

 longer be any doubt that, as regards the central connexions, the two nerves agree 

 very closely, consequently they must agree in function ; and as regards their peri- 

 pheral connexions, the two nerves differ, consequently they must differ in functions. 



By an oversight, which will one day excite surprise, physiologists, while insisting 

 on the peripheral differences in the two nerves, have, without one exception, disre- 

 garded the important fact of the central agreements. No one has investigated the 

 minute anatomy of the spinal cord without being aware that both anterior and 

 posterior nerves are in direct connexion with its grey matter; yet the conclusion has 

 been overlooked that if both are in direct connexion, both must play upon and excite 

 the sensibility of this grey matter. Were the properties of the two nerves different, 

 it would be intelligible that their effects on the centre should differ ; but as their 

 properties are similar, their effects on the centre must be similar. 



Logic forces the conclusion, that, in as far as the central connexions of the two 

 nerves are similar, their functions are similar; but inasmuch as their perij>hcral 

 connexions differ, their functions will differ. The function of moving a muscle is 

 assigned to those nerves which are connected with muscles ; the function of trans- 

 mitting impressions of touch, temperature, &c, is assigned to the nerves connected 

 with the surfaces. 



Thus the posterior nerves are sensory because they are related to a sentient centre. 

 They are also motory, because they are related, though in but a trifling degree, to the 

 muscular fibres distributed through the skin; and these they excite to contractions. 

 The anterior nerves are motory because the}' are related to muscles. They are also 

 sensory, because, like the other nerves, they are related to a sentient centre. In • 



