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

certain that all their movements are reflex actions aroused by the medium in which they live, and directed by habit. They only move now automatically.

Like the spinal cord and the motor nerves, the brain possesses the power of transmitting mechanical or electrical stimuli applied to it. But it is easy to foretell what effects the stimulation of a nerve will produce on the organs of movement, for we know exactly to what muscles this nerve is distributed, while it is difficult to specify the effect of a motor stimulus applied to the brain. In fact we do not always know which groups of muscles correspond to the nerve-fibres which we stimulate. Hence the often unexpected, and sometimes very remarkable results of wounds of the brain.

While out shooting, we sometimes see wounded animals make singular movements.

A partridge, for instance, wounded in a particular part of the head, rises all at once vertically to a great height in the air, and falls back dead.

We once observed a wounded hare turning round and round with great rapidity. The movement was made round the longitudinal axis of the body; that is to say, the animal seemed to revolve round a rigid rod, traversing it from head to tail. We thought at first that the wounded hare was endeavouring to run away, and we were surprised at the awkwardness of its attempts to escape. But we were soon convinced that these singular revolutions were quite involuntary; they were produced by an irresistible impulse. The hare had received a shot in the head, and this shot, perforating the skull, had injured one of the crura of the cerebellum. The shock received by the motor nerve-fibres had stimulated all the muscles with which they were connected, and these muscles, contracting all together, had produced in the animal a gyratory movement with which the will had nothing to do.

Other wounds of the brain can produce various motor phenomena which are no less surprising, Thus, by puncturing certain definite points of the encephalon, we produce what are known as circus movements, in which

the wounded animal does not turn on its own axis, but goes round and round like a horse in a circus.

The physiological explanation of these movements is still unsatisfactory, but they undoubtedly show that a stimulus applied to a single very localised part of the brain can produce contractions of several groups of muscles at once.

We see then, that owing to a peculiar anatomical arrangement, a great number of motor nerve-fibres, radiating towards different muscles, can start from the same very limited area of cerebral substance. In this manner a stimulus, which acts on a very small surface of the organ, can be simultaneously transmitted to several groups of muscles, just as by means of the multiple communication established by a network of wires, a single button can throw into action the bells of several electric apparatus.

In 1874, Ferrier showed that by applying an electric stimulus to certain cerebral convolutions, movements were produced in the eyes, the tongue, or the neck of the animal under experiment. He has called these

regions of the brain to which appear to converge a number of motor nerve-fibres, corresponding to welldetermined, and sometimes very extensive muscular groups, motor centres.

Bartholow, an American doctor, with a disregard for the human subject to which we have not yet attained in Europe, has reproduced on a man whose brain was exposed by a gun-shot wound, the experiments which Ferrier made on dogs. He has been able to prove that in man, as in other animals, there are motor centres, circumscribed areas of the brain, which have under their control the movements of particular regions of the body.

The localisation of the motor power for a whole group of muscles in a limited region of the brain, explains the common action of certain muscles, and the difficulty experienced in making one muscle act without another. The will, for instance, is unable to produce an isolated contraction in a single flexor, or a single extensor muscle When the will commands, it is obeyed