George Henry Lewes

“ 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. ”

“ If any one conceives that the anterior roots send forth nerves having a Neurility as widely opposed to that of the nerves issuing from the posterior roots as Motion is to Sensation, let his evidence be produced. If he conceives that the anterior nerves will only act in one direction, and the posterior in another and contrary direction, so that the motor nerve cannot excite a centre, and the sensory cannot excite a muscle or a gland, let him produce his evidence. ”

“ The functions of various nerves, that is to say, the uses they serve in the mechanism, depend upon their anatomical connexions. A nerve that is not distributed to a muscle cannot be expected to have a motor function; a nerve that is not distributed to a gland cannot be expected to have a secretory function; a nerve that is not distributed to an organ of sense cannot be expected to have a function of special Sensation. ”

“ It is true that division of the trunk does not wholly suspend the secretion; but that is because the influence of a nerve upon the gland is only that of a stimulus. Let the part played by the nerves be never so small, the fact that some influence over the secretion is exercised by them, proves that they transmit a stimulus from the centre to the organ—they act centrifugally; which is precisely the character claimed for a motor nerve. What the nature of the influence may be which nerves exercise on glands is still a mystery ”

“ For example, it is difficult to come to an understanding respecting the motor and sensory nerves, so long as we continue to talk as if we believed that "motility" resides in the spinal chord, and that the posterior roots are "sensitive." Motor force no more resides in the spinal chord, than explosive force resides in the lighted match; the motor-force is in the muscles, the explosive force is in the gunpowder ”

“ If, therefore, Sensibility is the property of Nerve-centres awakened by the stimulus of Neurility—if both nerves are in direct anatomical connexion with their centres—and if there be not two different kinds of Neurility, acting in very different ways upon the centre—there is no alternative but to accept the conclusion that both nerves have a sensory function. ”

“ Neither motions nor sensations belong to the nerves themselves, but to the muscles and centres, stimulated by the nerves. It is only in the looseness of unsystematized phraseology, that we speak of "sensitive impressions" being "conveyed to the brain;" and of "motor-impulses" being "conveyed to the muscles;" it is the stimulated nerves which excite the activity of brain and muscles, as the spark excites the explosive activity of gunpowder. ”

“ Todd, "between a motor and sensory nerve as regards structure. We can attribute the difference of endowment of the fibres to no other cause but to the nature of their peripheral and central connexions. The same nervous force is propagated by the fibres of each kind; but whether that force is to excite motion or sensation, must depend on the connexion of the fibres with muscles in the one case, and with the centre of sensation in the other." [5] The principle here laid down is irreversible; but it is an error to suppose that only one of the nerves is in connexion with the centre of sensation. ”

“ That all nerves may be, and that most are, double in function, the muscle-nerve being predominantly motor, because distributed to motor organs, whereas the skin-nerve is only distributed to the minute muscles of the skin, may be inferred from the anatomy of the invertebrata, in whom no double roots exist. ”

“ The discussion is one which cannot be without service; and if any champion of Bell's doctrine will do me the honour to descend into the arena, he may be assured that the harder he hits (without foul blows) , the more welcome he will be. ”

“ Of two bars of steel, one may have a magnetic property, and the other none, yet you cannot on mere inspection detect any difference in their structure. Of two tissues, one may be dead, and the other living, yet you cannot detect a difference." We do not know that two muscles, or two secreting cells, may not be so different in structure as to have different properties; but until this is proved, we are not warranted in assuming it. All we do know of the nerves points to their identity: they have the same physical, electrical, and chemical properties ”