Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/299

ANIMAL MAGNETISM.] MAGNETISM ganglia in its substance by which its rhythmic contractions are maintained. Further it is supplied by the vagus or pneumogastric nerve and by the sympathetic. Section of the vagus is followed by quickening of the heart s action, and stimulation of the lower end causes slowing and, if the stimulation be strong enough, stoppage of the heart, not, however, in a tetanic state (which would be the case if the fibres of the vagus acted directly on the muscular structure of the heart, as a motor nerve), but in a state of complete relaxation or diastole. Opposite results follow section and stimulation of the sympathetic fibres. It has been clearly made out that the terminal fibres of both nerves do not act on muscular fibres but on ganglion cells, those of the vagus " inhibiting " or restraining, whilst those of the sympathetic "accelerate" the action of the cells. Inhibition is now known to play an important part in all nervous actions, and it would seem that any power ful impression in a sensory nerve may inhibit or restrain motion. This is strikingly seen in some of the lower animals. A ligature applied loosely round the thigh of a frog whilst it lies on its back apparently deprives it of all power of motion. The weak sensory stimulation in this case seems to stop voluntary motion. Pressure on the internal organs of such animals as the rabbit, although gentle, sometimes causes paralysis of the lower or hinder limbs. Again, it has been ascertained that, whilst the spinal cord is the chief reflex centre, the reflex activity can be inhibited by impulses transmitted to it from portions of the cerebral hemispheres which are in a state of high activity. It would appear then that, if we suppose one set of sensory or recipient cells in the brain to be brought into a state of exalted irritability by the preliminary operations of hypnotism, the result might be inhibition of the parts devoted to voluntary movement. In like manner, the activity of sensory nerve cells may become inhibited. Thus stimulation of a certain cutaneous area, say the arm, by a mustard plaster, has been found to lower the sensi bility of the corresponding portion of skin on the opposite arm. The theory then offered is that " the cause of the phenomena of hypnotism lies in the inhibition of the activity of the ganglion-cells of the cerebral cortex, . . . the inhibition being brought about by gentle prolonged stimulation of the sensory nerves of the face, or of the auditory or optic nerve." According to this view, the portion of the brain devoted to voluntary movements is as it were thrown out of gear, and the movements that follow, in the hypnotic state, are involuntary, and depend on impressions made on the senses of the patient. To understand how this is possible, we must now consider shortly some of the views presently held as to the action of the brain. The researches of Hitzig, Fritsch, Ferrier, Hughlings Jackson, and many others indicate that certain movements initiated as a consequence of perception, and of the ideas thereby called forth, are due to nervous actions in the grey matter in certain areas on the surface of the cerebral hemispheres, and that there is another class of movements which do not require the agency of the cortex of the brain, but depend on the activity of deeper centres. These deeper centres are the optic thalami, which receive sensory impressions from all parts of the skin ; the corpora quadrigemina, which receive luminous impressions from the retina ; and the corpora striata, which are the motor centres whence emanate influences passing to the various groups of muscles. No doubt other sensory centres exist for hearing, taste, and smell, but these have not been clearly ascertained. In the case of conscious and voluntary movements carried out as the result of external impres sions, the excitation would pass first to the thalami optici (tactile) or corpora quadrigemina (visual), thence to the 281 cerebral hemispheres, where ideas would be called forth and volitional impulses generated; these would then be transmitted downwards through the corpora striata (motor) to the crura cerebri and spinal cord, and from thence to special groups of muscles, thus causing specific movements. Suppose now that the portions of cerebral hemispheres connected with ideation and volition were thrown out of gear, and that a similar sensory impression was made on the person ; again the path of nervous impulses would be to the thalami optici (tactile) or corpora quadrigemina (visual), and from thence directly through corpora striata (motor) to crura cerebri and spinal cord, then passing out to muscles, and causing movements as precise as those in the first in stance, and apparently of the same character. The difference between the two operations, however, would be this : in the first there would be movements following perception, idea tion, and volition ; in the second the same class of move ments would be effected by an automatic mechanism without any of the psychical operations above alluded to. This theory has the merit of simplicity, and is in accordance with most of the facts. The chief difficulty in the way of accepting it is to understand why, if hypnotism be so induced, it is not induced much oftener. One would suppose that, if gazing at a coin and having a few passes made with the hand were sufficient to bring about physiological changes of such importance, men would be oftener hypnotized in daily life than they are. But it is to be remembered that attention is seldom fixed on one object so long as in the experiment of producing hypnotism. The first occasion the experiment is made, even with so-called susceptible persons, the time occupied may be from 10 to 20 minutes, and during all that time the attention is on the strain, and feelings of fatigue are excited in the way above described. Again it is well known that sudden and strong sensory impressions often paralyse voluntary action for a time, even in ordinary life, and what is called "presence of mind " really means that power of self-control which prevents the bodily energies being paralysed by strong sensory impressions. A carriage bearing down on a nervous lady in a crowded street may deprive her of all power of movement, or she may automatically run here or there in obedience to the shouts of the bystanders ; but one with coolness can thread her way among the vehicles without fear or trouble. A hypnotized person is therefore to be regarded as an automaton. " To cause him to move his arm, the image of a moving arm must pass over his retina, or an unconscious sensation of motion must be induced through passive movement of his arm." 2. Insensibility to Pain. It has often been noticed that in the mesmerized or hypnotized person there may be complete insensibility to pain, so that deep pricks with a needle are not felt. During deep hypnotism a pin may be run into the hand without pain, but pain will be felt on awaking, and pulling out the pin in the waking state will cause acute pain. It would appear that certain nerves may convey tactile sensibility whilst others convey only painful impressions, and in certain forms of paralysis the patient may have tactile sensibility without pain, or the reverse. In hysterical women, as has been shown by Charcot and others, disorders of sensibility of this kind are not uncommon, indicating changes in the nervous centres. 3. Increased Reflex Spasm of Muscles. One of the most striking phenomena of the hypnotic state is the ease with which certain voluntary muscles may be rendered stiff. For example, if the operator stroke the skin over the biceps muscle in the upper arm, the limb will be at once power fully flexed, and the biceps can be felt stiff and rigid. To understand the physiological explanation offered of this

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