The biological theory of sleep considers all the other theories, while formulating its own, because biology considers the whole organism and not only one organ or function of the body. From a different point of view Binns’ theory is confirmed by Claperède, who points out that, “biologically regarded, sleep has its significance not as a passive state, but as an active instinct, like all the other instincts of animal life.” There is a degree of satisfaction to be found in this theory. It might be stated in this way, that, when man has had during any period all the sensations and experiences he can digest, the instinct to sleep takes possession of him. It is not that he becomes helpless in the hands of those experiences, but that his whole nature, like his stomach, knows when it has had food enough, and desires time for digestion and assimilation before it takes in more. Obviously, “utter separation from the phenomenal world,” as John Bigelow expresses it, becomes necessary. In his lectures on Botany at the Royal School of Medicine in Great Britain, Professor Leo H. Grindon said: “Man is captured in sleep not by death but by his better nature; to-day runs in through a deeper day to become the parent of to-morrow, and to issue every morning, bright as the morning of life, and of life-size, from the peaceful womb of the cerebellum.” This is the result not of a passive state, but of an active instinct; it accepts sleep as a time of growth, not merely a time of rest. Bigelow says, “Something goes on during sleep which is a preventive as well as an antidote to mania,” and, in furtherance of this same idea, Dr. J. J. G. Wilkinson of the Royal College of Surgeons of London, argues that it seems “as if a reason more perfect than reason, and uninfluenced by its partialities, had been at work when we were in our beds.” Even “biologically regarded,” Bigelow is not far astray when he claims that “our desire for sleep is manifestly designed to promote in us the growth and development of spiritual graces.” In other words, we desire to sleep, that we may relate the experiences of our every-day active life to the sum of knowledge we already possess by inheritance and past experience, that we may thereby get a fuller understanding of life and its purposes.