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Cantharides also stimulates the reflex function; when administered to a patient whose spinal cord had been divided by a tumour, it restored the retentive power of the neck of the bladder, which had been lost. It has been remarked that the cord of the frog has greater purposive power than that of man, as when all connexion with the brain, where all instinctive and co-ordinating faculty is supposed to reside, is cut off, the animal will leap and try to escape any irritation applied to the feet; while the movements in man are purposeless although powerful. Decapitated frogs have been seen to swim vigorously.
Besides the examples given of reflex action occurring without sensation, the often-quoted one of the sleeping child grasping thejfinger placed within its hand, may be alluded to, and the well-known fact that soldiers during a fatiguing march will walk, though quite asleep, when the sensorium is inactive. 2. As regards the conducting office of the cord, the functions of the antero-lateral and posterior columns respectively, are much less positively known than those of the roots of the nerves, which are both connected with the former. Sir C. Bell announced, shortly after his brilliant discovery regarding the
A xi_ A Ai i. i A i Diagram of course of Nerve Fibres
roots, that the antero-lateral i„ card.
Column Was exclusively motor, <""' interior root. pr. Posterior , •* 'root. g. Ganglion. mo. Medul
postenor, sensitive; but la oblongata."
1, 2, and 3 repre
Mr. Shaw, his son-in-law, who XTMt$%?L'SSfSt edited his works, states that m the cord. he afterwards saw reason to doubt the latter part of the hypothesis. It is shown to be untrue by the fact that the posterior column is traced into the cerebellum, which is certainly connected more with motion than sensation; and that if it be divided, all parts behind, instead of being rendered anaesthetic, become hyperaesthetic, or many times increased in sensibility—an effect due to the increased flow of blood which ensues from section of the vaso-motor nerves. Broum-Sequard, from whose work the foregoing diagram is copied, has shown that the sensitive fibres of the posterior root (pr.) cross to the opposite side of the grey matter of the cord, and so run up to the brain. The fibres of the anterior roots (ar.), on the contrary, do not decussate till they arrive at the pyramids. The arrows in the diagram indicate the centripetal direction of sensation, and the centrifugal direction of the motor force. These facts he has demonstrated by 3 sections: 1. Complete section of one half of the cord in the dorsal region. The effects on the limbs behind the section may be thus tabulated:
On injured side. On uninjured side.
2. The preceding section having been made, the opposite half is severed completely in the cervical region, and the sensibility of the limb, which was retained after the first section, is now lost. 3. The lumbar part of the cord is divided from its anterior to posterior fissure, and all sensitive fibres which come from the hind limbs and cross each other in the commissure being divided, all sensibility of these members is destroyed, but motion remains. The decussation of the sensitive fibres along the cord, and of motor ones only at the medulla oblongata, would account for the anomalous case recorded in the French translation of Sir C. Bell's work, where an injury to the spine produced paralysis of one limb and anaesthesia of the opposite. Half the cord was probably severed. Brown-Sequard concludes, from experimental and pathological proofs, that the grey matter and not the posterior columns, as believed by Longet, are the conductors upwards of sensibility.
There is no evidence to support Valentin's theory that the anterior column presides over flexion, posterior over extension, nor that which assigns the control over these movements to the upper and lower halves of the cord respectively. There is much pathological and other evidence to support the views of Todd and Bowman, who regard the posterior column as "in part commissural between the various segments of the cord, and in part subservient to the function of the cerebellum in regulating and co-ordinating the movements necessary for perfect locomotion," to which, I may add, that it may be the conductor of muscular sense to the cerebellum, where we shall show that that power resides.
The Roots of the Spinal Nerves are two—an anterior—small, white, and motor; and a posterior—larger, grey, and sensitive, forming also a ganglion, after which it is joined by the anterior. A filament from the sympathetic is sent to all these ganglia. The nerve-tubes of both roots are continuous in loops in the grey matter of the cord. The great physiological facts that the anterior roots are motor, the posterior sensitive, and the branches compound, were the discoveries of Sir C. Bell. In a rabbit (but from the greater period excitability lasts, its few nerves, and the wide space in the canal by the side of the cord, the frog is fitter for experiment) he divided the anterior roots on one side, the posterior on the other; irritation on the side where posterior roots were divided produced no effect, as the impression could not be carried up; but when applied to the other side, there were wincing, cries, and other evidences of pain, as the impression was conducted to the cord, and produced on the other side vigorous movements. This simple but beautiful experiment, besides demonstrating the respective functions of the roots, proves that sensi
tive impressions are transmissable from one side to the other of the cord.
Irritation of the detached portion of the anterior root
The Spinal Cord, its Membranes and Nerve- Hoots. a. The con', b. Dura mater, c. Denticulate ligament, d. Posterior or sens.ticc roots cut on the right side. e. Entire on the left of the anterior or motor roots, h. The ganglia on the posterior rsots, beyond which the anterior roots unite to them, to divide again into anterior and posterior branches.
will produce motion—but of the posterior root, no effect. The function of a nerve may be also gathered from its distribution—if to a muscle, it must be motor; if to skin, &c., sensitive. The fact that there is muscular