Page:Popular Science Monthly Volume 1.djvu/426

412 older men called it "stimulus" from without, is also undergoing rest and repair, so that when it comes again into work it may receive better the impressions it may have to gather up, and influence more effectively the muscles it may be called upon to animate, direct, control.

Thirdly, although in the organism during sleep there is suspension of muscular and nervous power, there is not universal suspension; a narrow, but at the same time safe, line of distinction separates the sleep of life from the sleep of death. The heart is a muscle, but it does not sleep, and the lungs are worked by muscles, and these do not sleep; and the viscera which triturate and digest food are moved by muscles, and these do not sleep; and the glands have an arrangement for the constant separation of fluids, and the glands do not sleep; and all these parts have certain nerves which do not sleep. These all rest, but they do not cease their functions. Why is it so?

The reason is, that the body is divided into two systems as regards motion. For every act of the body we have a system of organs under the influence of the will, the voluntary, and another system independent of the will, the involuntary. The muscles which propel the body, and are concerned in all acts we essay to perform, are voluntary; the muscles, such as the heart and the stomach, which we cannot control, are involuntary. Added to these are muscles which, though commonly acting involuntarily, are capable of being moved by the will: the muscles which move the lungs are of this order, for we can if we wish suspend their action for a short time or quicken it; these muscles we call semi-voluntary. In sleep, then, the voluntary muscles sleep, and the nervous organs which stimulate the voluntary muscles sleep; but the involuntary and the semi-voluntary muscles and their nerves merely rest: they do not veritably sleep.

This arrangement will be seen, at once, to be a necessity, for upon the involuntary acts the body relies for the continuance of life. In disease the voluntary muscles may be paralyzed, the brain may be paralyzed, but, if the involuntary organs retain their power, the animal is not dead. Sir Astley [sic] Cooper had under his care a man who had received an injury of the skull causing compression of the brain, and the man lay for weeks in a state of persistent unconsciousness and repose; practically he slept. He did not die, because the involuntary system remained true to its duty; and, when the great surgeon removed the compression from the brain of the man, the sleeper woke from his long trance and recovered. Dr. Wilson Philip had a young dog that had no brain, and the animal lay in profound insensibility for months, practically asleep; but the involuntary parts continued uninfluenced, and the animal lived and, under mechanical feeding, grew fat. Flourens had a brainless fowl that lived in the same condition. It neither saw nor heard, he says, nor smelled nor tasted nor felt; it lost even its instincts; for however long it was left to fast, it never voluntarily ate; it never shrunk when it was touched, and, when attacked by its fellows,