occur.

that make up the cerebro-spinal axis,-the brain and spinal cord. These central masses all contain grey substance, the cellular or vesicular matter, wherein the nerve fibres are known, in some cases if not all, to terminate. None of them is exclusively composed of grey matter, for within the boundaries of each mass a quantity of the communicating fibres But their peculiar or distinctive character is imparted by the grey substance that they contain. By setting forth the ascertained functions of these masses in succession, we shall arrive at some notion of the powers and properties of the grey matter, just as in discussing the nerve fibres we have obtained a knowledge of the use of the white substance whether in the nerve ramifications, or in the interior of the centres.

17. With regard to the Spinal Cord, we find, in the first place, that it is necessary to sensation and to voluntary movement (movement from feeling) throughout the entire trunk and extremities of the body. If the cord is cut across at any part, all feeling is lost, and all power of movement by the will, everywhere below that place, or in every portion of the body where the nerves arising beyond the cut are distributed. If the division is made far down in the back, the lower limbs are the parts principally paralysed; from them feeling comes no more, nor is it possible to move them by any mental effort. If the cut is in the neck, the arms, trunk, and legs are alike paralysed. It becomes evident that the continuity of the cord with the brain is necessary in order to connect the mental system with the bodily members. The cord by itself will not give the power either of sensation or of voluntary movement. We must regard this portion of the cerebro-spinal axis as a main channel of nervous conveyance for sensation and voluntary action, between the brain, and the trunk, and extremities of the body. The nerve ramifications are here, as it were, gathered together into one rope or bundle for convenient transmission to and from the masses of the encephalon. To this extent, the cord is not a centre, but an assemblage of the general system of ramifying or com

THE SPINAL CORD A CENTRE.

45

municating fibres; we may look upon it as the trunk of the tree, the final stream of the river system.

If now we make experiments upon the cord when dissevered from the brain, we discover that a power of producing movements, though not voluntary, still remains. On irritating any portion of the substance, movements of the limbs are observed. This effect might, no doubt, arise from the continuity of the part with some of the motor nerves; for we have seen that movements in a limb are caused by pinching one of the nerves that supply the limb. But there is a mode of trying the experiment so as to prove decidedly that the spinal cord is itself a source of movement; that is, to prick the skin of the toes; when this is done we find that a convulsive stimulus instantly returns upon the limb and throws it into action. Hence we infer that an impression arising on the surface of the body and conveyed to the spinal cord, but not to the brain, causes the cord to send forth a motor stimulus to the moveable organs, a phenomenon, moreover, that ceases on the destruction of the cord.

'In most instances where the spinal cord has been divided, whether by design or accident, it has been found that although the will cannot move the paralysed parts, movements do occur in them of which the individual is unconscious, and which he is wholly unable to prevent. These take place sometimes as if spontaneously, at other times as the effect of the application of a stimulus to some surface supplied by spinal nerves. The apparently spontaneous movements frequently resemble voluntary actions so closely, that it is almost impossible to distinguish them.'

The following experiments serve to illustrate these

actions:

'If a frog be pithed by dividing the spinal cord between the occipital hole and the first vertebra, an universal convulsion takes place while the knife is passing through the nervous. centre. This, however, quickly subsides; and, if the animal be placed on the table, he will assume his ordinary position of rest. In some exceptional cases, however, frequent combined movements of the lower extremities will take place for a longer

or shorter time after the operation; when all such disturbance has ceased, the animal remains perfectly quiet, and as if in repose, nor does there appear to be the slightest expression of pain or suffering. He is quite unable to move by any voluntary effort. However one may try to frighten him, he remains in the same place and posture. If now a toe be pinched, instantly the limb is drawn up, or he seems to push away the irritating agent, and then draws up the leg again into its old position. Sometimes a stimulus of this kind causes both limbs to be moved violently backwards. A similar movement follows stimulation of the anus. If the skin be pinched at any part, some neighbouring muscle or muscles will be thrown into action. Irritation of the anterior extremities will occasion movements in them: but it is worthy of note, that these movements are seldom so energetic as those of the lower extremities.'-TODD and BOWMAN, L, 308-9.

These experiments prove beyond a doubt that a circle of nervous action is completed by the spinal cord in its isolation from the brain. It is manifest that the in-carrying nerves must be in communication with out-carrying or motor nerves, in the interior of the spinal substance, a communication that renders the cord, to all intents and purposes, a nerve centre, and not merely an aggregate or bundle of nerve conductors. This property of sending out motor power is believed to depend upon the grey matter that is enclosed in the cord; for no reflex force is ever shown without the intervention of a certain portion of grey substance; and such reflected power is more energetic as the grey or vesicular matter exists in larger quantity. The cord is therefore one of the power-originating portions of the nervous system; and investigation has determined pretty accurately what kind of power it yields, and for what purposes in the animal economy. I shall here present a brief summary of the principal active functions sustained or assisted by the central energy lodged in this part.

18. In describing the functions of the cord it is convenient to include the Medulla Oblongata, with which the cord is continuous in structure, and which is found to possess the same

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brain, we spent 1 va trat nede trabest a be drawn acrvire vin dhe per-crni ana bervien the seat of simt ai anime viibim feeing and the seas of stimuli and actions with feeling; berveen the inrimany and the voly-terveen body and mind. The actions maintained by the øred and mednia solongana resemble many of the true metal acorns: they are the same mosties, the same moveable para bus imammoth as they do not require feeling as an indigenable acima of their performance, they are excluded from the province, marked by cur definition of mind. They are termed automatic or self-moved actions and also refer actions. The enumeration of the functions of the cord will be an enumeration of this class of actions which seem to be mental but are not.

(1.) Movements connected with the process of Digestion. This process requires a series of movements to be kept-up for passing the food along the different stages of the alimentary canal, to undergo its various changes there. The first operation upon the food in the mouth,-the chewing and masticating-is voluntary, and requires the stimulus of the brain. On passing to the back part of the tongue, the food enters the bag of the throat, or pharynx, and is thence projected down the gullet by contractions and movements that are involuntary ; the mind has no control over them, and scarcely any feeling or consciousness of their taking place. These movements are due to the medulla oblongata. The contact of the food with the surface of the throat makes an impression on certain nerves distributed on that surface; these nerves transmit an influence to the medulla oblongata, and there returns a stimulus to the muscles of the pharynx, which muscles are in connexion with the same centre through motor nerves. In

this manner, the food is propelled onwards by the muscular contractions of the tube, and enters the stomach. The mind is utterly excluded from participation in this effect, being unable either to assist or retard the progress of the mass, and except at the two extremities, being hardly aware of the stage that is reached at any moment. This function illustrates what is often said of the medulla oblongata and the cord, that they give birth to the movements necessary for keeping up the organic processes.

(2.) Connected with the Respiration, there are certain reflex, or automatic, movements. The action of breathing is performed by means of a number of muscles, but these, unlike the muscles of the alimentary region, are also the instruments of the will in voluntary operations. The muscles of the chest and abdomen are employed in the acts of breathing; in taking in breath the lungs are expanded by the muscles of the chest, and in expiration the abdominal muscles contract the chest and force out the contained air. This action goes on whether we wake or sleep, being involuntary, and the seat of power in this case is found to be the medulla oblongata. There passes to and fro, between the muscles and the grey matter of the medulla, a nervous stimulus; the two opposing sets of muscles are acted on by turns, and an alternating movement is thus kept up from the first moment of drawing breath to the last. There is more here than a simple reflex stimulus, such as described in the actions of a pithed frog. The case is not one where irritation or contact with a surface, excites a single group of muscles in one way, as when the frog's limb is drawn up on the pinching of the toe. We have a higher complication, a stage in advance towards combined and regulated action, the kind of action that attains its highest pitch under the mental organization, being developed to some small extent within the automatic, or spinal system. In the propulsion of food there is in reality a compound or double action, a contraction along the length of the gut with a contraction of the thickness, and this action follows a certain order or rhythm so as to move the food always in one way; but in breathing the compound action is of a more decided and palpable kind, inas