What does all this mean? I will refer to one or two facts in relation to the structure and function of the brain, and show one or two simple experiments of very ancient parentage and date, which will, I think, help to an explanation. First, let us recall something of what we know of the anatomy and localisation of function in the brain, and of the nature of ordinary sleep. The brain, as you know, is a complicated organ, made up internally of nerve masses, or ganglia, of which the central and underlying masses are connected with the automatic functions and involuntary actions of the body, while the investing surface shows a system of complicated convolutions rich in grey matter, thickly sown with microscopic cells in which the nerve ends terminate. At the base of the brain is a complete circle of arteries, from which spring great numbers of small arterial vessels carrying a profuse blood supply throughout the whole mass, and capable of contraction in small tracts, so that small areas of the brain may, at any given moment, become bloodless, while other parts of the brain may simultaneously become highly congested.

Now, if the brain, or any part of it, be deprived of the circulation of blood through it, or be rendered partially bloodless, or if it be excessively congested and overloaded with blood, or if it be subjected to local pressure, the part of the brain so acted upon ceases to be capable of exercising its functions. The regularity of the action of the brain and the sanity and completeness of the thought which is one of the functions of its activity, depend upon the healthy regularity of the. quantity of blood passing through all its parts, and upon the healthy quality of the blood so circulating. If we press upon the carotid arteries which pass up -through the neck to form the arterial circle of Willis, at the base of the brain, within the skull - of which I have already spoken, and which Supplies the brain with blood - we quickly, as everyone knows, produce insensibility. Thought is abolished, consciousness is lost. And if we continue the pressure, all those automatic actions of the body - such as the beating of the heart, the breathing motions of the lung, which maintain life and are controlled by the lower brain centres of ganglia - are quickly stopped, and death ensues.

We know by observation in cases where portions of the skull have been removed, either in men or in animals, that during natural sleep the upper part of the brain - its convoluted surface, which in health and in the waking state is faintly pink like a blushing cheek, from the colour of the blood circulating through the network of capillary arteries - becomes white and almost bloodless. It is in these upper convolutions of the brain, as we also know, that the will and the directing power are resident; so that in sleep the will is abolished and consciousness fades gradually away as the blood is pressed out by the contraction of the arteries. So, also, the consciousness and the directing will may be abolished by altering the quality of the blood passing through the convolutions of the brain. We may introduce a volatile substance, such as chloroform, and its first effect will be to abolish consciousness and induce profound slumber and a blessed insensibility to pain. The like effects will follow more slowly upon the absorption of a drag, such as opium; or we may induce hallucinations by introducing into the blood other toxic substances, such as Indian hemp or stramonium.

We are not conscious of the mechanism producing the arterial contraction and bloodleesnees of those convolutions related to natural sleep. But we are not altogether without control over them. We can, we know, help to compose ourselves to sleep, as we say in ordinary language. We retire into a darkened room, we relieve ourselves from the stimulus of the special senses, we free ourselves from the influence of noises, of strong light, of powerful odours, or of tactile impressions. We. lie down and endeavour to soothe brain-activity by driving away disturbing thoughts, or, as people sometimes say, 'try to think of nothing/ And, happily, we generally succeed more or less well. Some people possess an even more marked control over this mechanism of sleep. I can generally succeed in putting myself to sleep at any hour of the day, either in the library chair or in the brougham. This is, so to speak, a process of self-hypnotisation, and I have often practised it when going from house to house, when in the midst of a busy practice; and sometimes I have amused my Mends and family by exercising this faculty, which I do not think it very difficult to acquire. Now there is something here which deserves a little further examination, but which it would take too much time to fully develop at present.

Most people know something of what is meant by reflex action. The nerves which pass from the various organs to the brain convey with great rapidity messages to its various parts, which are answered by reflected waves of impulse. If the soles of the feet be tickled, contraction of the toes, or involuntary laughter, will be excited, or perhaps only a shuddering and skin-contraction known as goose-skin. The irritation of the nerve end in the skin has carried a message to the involuntary or the voluntary ganglia of the brain, which has responded by reflecting back again nerve-impulses which have contracted the muscles of the feet or the skin-muscles, or have given rise to associated ideas and explosion of laughter. In the same way, if during sleep heat be applied to the soles of the feet, dreams of walking over hot surfaces - Vesuvius or Fusiyama, or still hotter places - may be produced, or dreams of adventure on frozen surfaces or in Arctic regions may be created by applying ice to the/feet of the sleeper.

Here, then, it is seen that we have a mechanism in the body, known to physiologists as the ideo-motor or sensory motor system of nerves, which can produce, without the consciousness of the individual, and automatically, a series of muscular contractions. And remember that the coats of the arteries are muscular and contractile under the influence of external stimuli, acting without the help of the consciousness, or when the consciousness is in abeyance. I will give another example of this, which completes the chain of phenomena in the natural brain and the natural body I wish to bring under notice in explanation of the true as distinguished from the false, or falsely interpreted, phenomena of hypnotism, mesmerism, or electro-biology. I will take the excellent illustration quoted by Dr. B. W. Carpenter in his old-time but valuable book on 'The Physiology of the Brain.' When a hungry man sees food, or when, let us say, a hungry boy looks into a cookshop, he becomes aware of a watering of the mouth and a gnawing sensation at the stomach.