be made as to their peripheral distribution?" An experiment will convince my critic that it is not only "possible" to separate the fibres, but that my "assumption" is easily demonstrated. Let him divide the anterior 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 anatomy 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 sensibility excited by the posterior, as the sensation of sound is unlike the sensation of light, which are nevertheless similar, in being both sensations."
I endeavoured to prove by experiment that it was through the anterior nerves that the "muscular sense" was excited. The evidence cannot 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, produces none of the ordinary signs of sensation; but the irritation of the posterior produces unequivocal signs of pain. This is held to be conclusive 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 sensations are as special as those of sight or hearing, and every special sense responds 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
