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Page:Popular Science Monthly Volume 46.djvu/242

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WE do not comprehend the mystery of wakeful consciousness; and therefore that of temporary unconsciousness, including sleep of all kinds, is equally beyond our understanding. To say that sleep is a suspension of our control over our thoughts and our motor nerves and voluntary muscles is a mere substitution of other classes of mysteries equally inscrutable.

The same should be frankly admitted as to all our so-called explanations of natural phenomena, which consist mainly of generalizations, expressing in few words the laws that rule and connect, so far as we can discover, the infinity of cosmical facts and transformations. Such generalizations—whose surpassing importance and value are nevertheless undeniable—imply, as essential preliminaries, the laborious classification of the facts in any field of investigation that we have in hand.

But in the field of which we are now to attempt a brief and necessarily superficial survey it must be conceded that such classification is as yet highly imperfect. The forms and modifications of existence varying in cause or origin, nature, and degree which may be called by the general name of sleep have not yet been subjected to the exact and critical experimental research needed for scientific classification. Little can now be done except to point out wherein our knowledge is defective, and to indicate some more or less tentative arrangement of the facts under different heads as a provisional guide to the study of this condition of existence, in which mos persons expend one third of their terms of life. Such heads may be as follows:

An attempt at a definition of normal healthy slumber, which only is entitled to be called—

"Tired Nature's sweet restorer, balmy sleep."

Such a definition must be sufficiently well founded on the conditions presented in natural sleep to admit of drawing lines of parallelism with and of divergence from other species of lethargy or unconsciousness, or modified consciousness, that arise from abnormal or morbid conditions, mental and nervous disorders, drugs, anæsthetics, cold, heat, exhaustion, partial asphyxiation by drowning or otherwise, etc.

A statement of our present narrow range of facts and observations relative to the chemical, physical, and physiological changes of the organs of the body, and of their functions, during normal sleep.

A consideration of the mental, moral, and emotional phenom-