Binns’ theory is that physiological sleep is in antagonism to intellectual activity, being the active process of nutrition, assimilation of food, or of the repair of the waste of the body; that it concerns the nerve centers: that is, “the ganglionic system.” It is a generally admitted theory that man’s activity, whether physical or mental, “uses up” tissue and nerve force, and that it is only when repair exceeds this waste that life is maintained at a high standard. If the activities of life be many and varied, much sleep according to this theory would be needed to repair the waste of force. Experience has shown that those who live purely physical lives, doing hard manual labor with little mental exercise, need the most sleep. Those whose activities are mostly mental generally sleep fewer hours, though the desire for sleep may be as intense when it comes as is that of the manual laborer. (See Appendix, Questionnaire.) Regarding sleep as a necessity, in itself an “active and positive faculty,” Binns says of it that “it is the true ‘vis medicatrix naturæ’ —the healing force of nature—to whose vigilance we are indebted for that condition of mind and body called ‘health.’” However, he is not an advocate of long hours of sleep for everybody. He thinks individuals differ widely in the amount of sleep needed. He makes the general statement that, “the lower the cerebral organs in the scale of organization, the greater the power of sleep.” On this point all the authorities agree, and even in our own experience we learn that. The animals nearest to man in point of development sleep more than man sleeps; and, among men, those who live the most sluggish mental and emotional lives sleep longer than those whose brains are more active. There may, of course, be exceptions to this rule, and yet those exceptions would not disprove that there is a rule. Much depends, says the good doctor, upon the peculiarities “of the individual; the culture of his mind; his amusement, his food, his occupation, and the temper with which he wooes sleep. General Elliot never slept more than four hours out of twenty-four, and his food consisted wholly of bread, vegetables, and water.” This seems like one more link in the chain that binds up our habits of eating with our power to sleep. Just as heavy eating late at night may so disturb our slumber as to leave us practically sleepless, so general heavy eating may render us so incapable of mental activity that sleep may take possession of us. General Elliot’s slight need of sleep was probably due, in large measure, to his light diet, and Dr. Binns seems to be of that opinion. We notice that flesh-eating animals, especially serpents, gorge and then sleep long.