Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

the muscles, by being directed to the segment of the cord whence their nerves proceed. All muscular movements, whether reflex, emotional, or voluntary, are immediately called into action by the same class of sensory or efferent nerve fibres ; moreover, the excitor or afferent fibres are at once iu like manner the chan- nels of the transmission of stimuli, which gives rise, in one instance, to reflex actions through the spinal cord, and of im- pressions, in another instance, that become sensations when transmitted to the sensorium. The mechanism, then, of a vol- untary action in these parts that are supplied by spinal nerves would be the following: — The impulse of volition, excited primarily in the brain, acts at the same time upon the gray matter of the cord, (through the fibres of the white substance of the brain, which radiate from the thalami optici and the corpora striata, or, according to Dr. Todd, simply through the strands of the medulla oblongata, especially the anterior pyramids,) and then from this gray mat- ter of the cord, simultaneously upon the anterior roots of the nerves implanted in it. This gray matter, in virtue of its asso- ciation with the brain by means of the fibres of the white sub- stance of the brain, or the anterior pyramids, becomes part and parcel of the organ of the " will" and therefore as distinctly amenable to acts of the mind, as that portion which is contained within the cranium. If we destroy the commissural connection with the brain through the pyramidal or white brain fibres, the spinal cord ceases to take part in or respond to mental nervous actions ; or, if that connection be only partially destroyed, then precisely that portion of the cord, which the now injured nerve fibres had formerly associated with the brain, is no longer influ- enced by the mind. Again, if the seat of volition in the brain be diseased, then the portion of the cord that corresponds to the seat of that lesion participates in the effects of the disease as far, at least, as regards voluntary actions. And again, we must bear in mind that a continuity of fibrous structure here is not absolutely necessary for the transmission of nervous energy, or, as Dr. Todd would say, ufor the excitement of nervous