ena presented in natural and in artificial sleep, including its morbid forms, with those forms in which the mind sleeps with the body awake, and those in which the body may sleep with the mind more or less awake.
Anæsthesia in general, inclusive of its widely differing successive stages, as that of exaltation of some mental faculties, with or without full consciousness, or one of the waking dream conditions (see further on—) that of extinction of full consciousness with the muscular system still awake—and, finally, that of complete lethargy of the mind and body with extinction of all sensation.
An attempt, which must needs yet be quite crude, to generalize something useful from the sparse and scattered array of facts thus found to be available.
As to a definition of natural sleep, it may be interesting to go back a century and examine the views then held. Having at hand the second edition of the Encyclopædia Britannica, published from 1778 to 1783, the writer finds therein an article on Sleep, in the tenth volume, which article is brief, being but supplementary to that on Dreams, in the fourth volume. To this latter subject we shall return further on. Under Dreams, the following meager definition of sleep is given: "Sleep is a state in which all communication is cut off between our sentient principle and this visible world." By this, taken literally, a blind man would be asleep. But, of course, the word visible was intended to imply the whole world of the senses. Still, allowing such latitude, the definition is both inaccurate and inadequate. As to the asserted complete cutting off of external impressions from the senses in true sleep: were this so, a sleeping person could not be awakened by the usual means—namely, a forcible external impression upon one or more of the senses.
Its inadequacy may be briefly illustrated by pointing out that it takes no note of one of the most salient phenomena of sleep—that the will, though not at all suspended therein, being easily recognized in dreams, altogether loses its rationality and its control over the workings of the mind as well as over those of the body.
The following may be set forth as an attempt at a reasonable and comprehensive definition, or rather description, of the conditions we find in sleep: Sleep is a state in which the impressions of external objects on the senses are dulled, but not annulled or suspended; in which the emotions, the imagination, the memory, and the will are but partially or even not at all suspended, and may even be intensified, while the control of the will over the emotions, the imagination, and the memory is wholly annulled,
