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 every one knows, produce insensibility. Thought is abolished, consciousness 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 lungs, which maintain life and are controlled by the lower brain centers 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 color 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 drug, 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 the bloodlessness 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 colors, or of tactile impressions. We lie down and endeavor 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-hypnotization, and I have often practiced it when going from house to house, when in the midst of a busy practice, and I sometimes have amused my friends and family by exercising this faculty, which I do not think it very difficult to acquire. (We also know that many persons can wake at a fixed hour in the morning by setting their minds upon it just