the connexion of the fibres with muscles in the one case, and with the centre of sensation in the other."[1] 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. I pointed out the fact, which had been universally disregarded, that the anterior (motor) roots were quite as unmistakeably in anatomical connexion with the ganglionic substance of the spinal chord, as the posterior roots were; and the conclusion seemed irresistible, that if one nerve in connexion with a centre will stimulate the activity of that centre, another nerve precisely analogous in structure, and endowed with an analogous property (propagating the same nervous force), if also in connexion with that centre, must also stimulate its activity. Modern microscopic researches have rendered the direct connexion of the anterior roots with the ganglionic substance, a fact beyond dispute. To resist the conclusion I have drawn, it. will be necessary to prove: 1st. That the ganglionic substance with which the anterior roots is connected has not the same property as the ganglionic substance of the posterior roots; or, 2nd. That nerves are only capable of stimulating in one direction. But it has been proved by Schiff that there is no difference between the properties of the anterior and posterior horus. And it has also been proved that nerves conduct in both ways.
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.
In vindicating the essential similarity of the two sets of nerves, we are not overlooking their specific diversity. 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.
Bell's discovery that the anterior roots ministered to motion, and the posterior to sensation, may be interpreted thus: the anterior nerves are muscle-nerves, the posterior are skin-nerves. My critic in the British and Foreign demurs to this. " It is known to every anatomist," he says, "that it is a pure assumption on the part of Mr. Lewes to assert that the fibres of the anterior roots are distributed exclusively to the muscles, and those of the posterior roots exclusively to the skin. How, we would ask, is it possible anatomically to separate the fibres of the anterior and the posterior roots in any nerve of mixed endowments? and on what basis, save that of physiological experiment, can any positive statement
- ↑ Todd, Physiol. of Nervous System, in Cyclopæd. of Anat. and Phys.
