shaped expansion called the motor end-plate, which is intimately connected with the enveloping sheath of the ultimate muscle fibres. The motor end-plate is the junction which unites nerve and muscle. By its means a communication is established between the motor organ and the conductor which conveys to it the orders of the will.

III.

The spinal cord seems to be formed by the union of all the nerves of the trunk and limbs. It has the shape of a thick white cord, in connection with which are both the motor and the sensory nerves, and which is continuous with the brain, of which it is in a certain sense a prolongation.

It is made up of two kinds of tissue: one is white like the tissue of the nerves, and the other has a grey colour. The white matter forms the external layers of the cord. It has the same elementary structure as the nerves and possesses the same conducting properties as these organs; but being formed of sensory as well as of motor fibres, it has mixed functions: the posterior region conducts sensory impressions, whilst the anterior region transmits motor stimuli.

As far as the white matter is concerned, the spinal cord does not differ at all from the nerves. If we make a transverse section, the voluntary movements of all muscles which receive their nerves from the cord below the section are abolished. If, however, we pinch strongly, or electrify the anterior tracts, we produce involuntary contractions in the muscles innervated by the points to which the stimulus is applied.

The grey matter makes the spinal cord a nerve-centre, that is to say, an organ capable not only of conducting a motor stimulus, but also of spontaneously bringing about a movement in the muscular system. It is made up of irregularly spherical cells which have filamentous processes putting them in communication one with the other, and anatomically and physiologically with the motor and sensory nerve fibres. The nerve-cell is the

most exalted element in the hierarchy of living tissues: when we find one in any part of the nervous system, we may be certain that this region possesses a power proper to itself and independent of any other part.

The special power of the spinal cord is shown by the faculty which it has of calling forth motor stimuli in the muscles without the help of the brain and without the order of the will.

Decapitated animals can make spontaneous movements, provided that their spinal cord is untouched.

A duck whose head has just been cut off flaps its wings and can even walk a few steps.

On the body of a man just decapitated, if we strongly pinch the arm or the leg, the limb is drawn away as if the executed man felt the impression received by the skin, and tried to escape from it.

All these movements have the appearance of voluntary movements; they are however unconscious and involuntary, like all those executed without the concurrence of the brain. To give an idea of the power of the spinal cord when reduced to its own resources and acting without the aid of the brain, we cannot do better than quote the following curious experiment :

"If we cut off the head of a frog, the animal jumps and twists for an instant, and then is still. It would for ever remain motionless if kept under a bell-glass, in a damp atmosphere, and sheltered from all stimulation. But if we touch one of its legs, or drop on it a little vinegar, the frog immediately tries to escape and to put at a distance the cause of disturbance. If the drop of vinegar is on the right leg, it endeavours to wipe it off with the left, and vice versa.”

At first sight this appears intelligent, and the frog seems to have made a conscious voluntary act; if however we continue the experiment we see that the movement of the decapitated frog is nothing but a mechanical response to a lively stimulus, and in no sense an action calculated with a view of escaping danger.

Goltz and Portes, having taken a frog, removed the brain and then plunged the animal into water in a

glass vessel. When touched, it swam as if to escape, and even jumped out of the vessel. But on warming the water very slowly, in such a manner as to reach a very high temperature without any abrupt transition, the frog did not move, nor try to jump out of the vase, but in the end was boiled without having made any action indicating a consciousness of danger."

The movements of a decapitated frog are reflex movements. In reflex movements the will has no place. That which excites the muscular action is a sensation which runs up the whole length of a sensory nerve to a given point of the spinal cord, from which a motor nerve starts. The end of the sensory nerve and the beginning of the motor nerve join in the same cell of the cord, from which is given off a third nervous filament in the direction of the brain.

When the sensory impression, in place of travelling towards the head by this third ascending filament, stops in the spinal cord, the latter sends it on transformed into movement in the direction of the muscle, whither it is conducted by the motor nerve. The impression is reflected at the motor centre and returns upon its steps instead of continuing its journey, just as are reflected the sonorous waves of the voice, which, striking against a wall, rebound to produce an echo.

We may say that a reflex movement is the echo of a sensory impression.

It is not necessary that the brain should be destroyed for the production of reflex movements: it is enough that it takes no part in the muscular action. This being the case, the latter is not willed and is produced unconsciously, as may be observed in a sleeping man, or even one preoccupied, who, according to a common expression, "has his head in the clouds," and does not think about what he is doing. We may constantly see a preoccupied man walk past his own doorway which he intended to enter. We say that he is distracted, and that his legs work with an automatic

*Mosso. La Peur.

movement.

This automatic movement of walking was at first very laboriously acquired by the infant, later it has become so easy of execution that the brain takes no part in it. The sensation which the ground produces on the sole of the foot resting on it determines, as a reflex effect, a movement of the other leg which comes in its turn to a position in front of the first, and so on. This regular succession of movements of the legs, which now rest on the ground, now are raised from it, can take place without the will playing any part in it, or the brain being conscious of it.

In bodily exercise a number of movements become automatic by habit, and it comes to pass that, during their performance, the will can be occupied about other things, without participating in the action of the muscles In this case the spinal cord alone presides over these movements without any intervention of the brain.

We shall have an opportunity, in discussing the therapeutical applications of exercise, of profiting by the summary of ideas we have just expounded. We shall show how important it is that a man suffering from mental overwork should seek by preference automatic exercises, which do not bring the action of the brain into play.

In many cases the spinal cord is able, thanks to its auto-motor power, to take the place of the brain, and preside alone over very complicated movements. But its absolute integrity is necessary for the performance of automatic or reflex actions. If a probe be thrust down the spinal canal of a recently decapitated frog, its reflex power is completely annihilated, consequent on the destruction of the cord, which is broken up by the instrument. At the same moment the animal loses all power of reaction to an agent which calls forth the sensibility of the skin: no movements can be produced in the limbs except by directly exciting the muscles or their motor nerves.

IV.

The Brain is a rounded, soft, greyish mass. It is composed, like the spinal cord, of grey and white matter, and like the cord, consists of nerve fibres and cells. But just the opposite of what we observed in the cord-the grey matter occupies the periphery, the cortex of the brain, while the white matter is in the centre: further, in the thickness of the white matter are important nuclei of grey matter, indicating the presence, in certain central regions of the organ, of nerve cells, foci of independent activity.

In the brain, as in the cord, the white matter conducts the stimuli it receives, while the power of sending forth spontaneous motor stimuli devolves on certain cells of the grey matter.

The grey matter of the brain can, like that of the cord, manifest its proper activity by reflex effects. The brain gives origin to motor and sensory nerves, and a sensory impression can give rise to a reflex movement in muscles supplied by cranial nerves. It is in this manner that, in a recently decapitated animal, a drop of vinegar applied to the surface of the eye produces a closure of the eyelids.

The brain is then, like the spinal cord, a centre of reflex motion; but it is further a centre of voluntary motion.

This is, from the point of view of movements, the characteristic of the brain: when the brain is removed, every willed muscular action disappears with it.

It is not necessary to remove the whole of the brain in order to deprive an animal of the power of manifesting its will by conscious actions. It is sufficient for this purpose completely to destroy the grey matter, for it is in the interior of this tissue that the voluntary stimuli, the nature of which is, up to the present time, unknown, are elaborated. It is practicable to keep dogs deprived of this part of the brain alive, and we may be