LEWES ON Tin: SENSORY AND MOTOR FUNCTIONS OF UEB.VES. 183 



be made as to their peripheral distribution ?" An experiment will con- 

 vince my critic that it is not only " possible" to separate the fibres, but 

 that my " assumption" is easily demonstrated. Let him divide the an- 

 terior roots of the nerves supplying one of the extremities of a frog, and 

 he will find that all the fibres in the muscles of that extremity degenerate, 

 but .none of those distributed over the sheath or to the skin. A more 

 absolute proof could not be required. I would further remark that it is 

 not enough for a nerve to pass through or along a muscle, its filaments 

 must terminate in the substance of the muscle, if its function is to be 

 motor. 



My critic is also inaccurate in stating that I attribute the difference 

 of function of the two nerves entirely to their peripheral distribution. 

 He should have said mainly; the difference in their central distribution is 

 insisted on, as one of the reasons why the muscular sensations differ from 

 the skin sensations. Both nerves are directly connected with the spinal 

 chord, and " both must, therefore, have a similar functional relation to 

 it." The critic should not have passed over the emphatic sentence of 

 the next paragraph, — " Observe, I say the relation is similar, not the 

 same. It requires but a moderate acquaintance with microscopic ana- 

 tomy to be aware that the anterior and posterior roots differ in their 

 distribution over the spinal chord ; indeed, it is partly on this difference 

 that I explain the different forms of Sensibility excited by each root. 

 But, underlying this diversity, there is a fundamental agreement. 

 Hence they may be called similar, though not the same. The form of 

 sensibility excited by the anterior root is as unlike the form of sensi- 

 bility excited by the posterior, as the sensation of sound is unlike the 

 sensation of light, which are nevertheless similar, in being both sensa- 

 tions." 



I endeavoured to prove by experiment that it was through the ante- 

 rior nerves that the " muscular sense" was excited. The evidence can- 

 not be reproduced here ; but, perhaps, for the sake of argument, the 

 reader will admit the point as proved, and we may then show that the 

 one objection which is always raised against the sensory function of the 

 anterior nerves falls to the ground. When both anterior and posterior 

 roots are divided, an irritation of the central ends of the anterior, pro- 

 duces none of the ordinary signs of sensation ; but the irritation of the 

 posterior produces unequivocal signs of pain. This is held to be con- 

 clusive against the sensory functions of the anterior root. But is it so ? 

 On the supposition that the anterior root serves the muscular sense, we 

 have no right to expect anything than what we find. The muscular sensa- 

 tions are as special as those of sight or hearing, and every special sense re- 

 sponds only in its special form: the optic nerve, when irritated, produces 

 sensation of light, but no pain ; the auditory nerve a sensation of sound, 

 but none of temperature, light, or pain. In like manner, the irritation of 

 a muscle-nerve will produce the sensations habitually produced by that 

 nerve, which are not those of pain. My assertion that muscular sensations 

 are not those of pain has been scornfully rejected, and a reference made 

 to the agonies of cramp. But cramp, I must maintain, with Schiff and 



