A gentleman recently under my care for a paralytic affection, informed me that he could at any time render himself sleepy by looking for a few minutes at a bright light, so as to fatigue the eyes, or by paying particular attention to the noises in the street, so as to weary the sense of hearing. It is well known that sleep may be induced by gentle frictions of various parts of the body, and doubtless the other senses are capable of being so exhausted, if I may use the expression, as to diminish the power of the attention, and thus lessen the demand for blood in the brain. As a consequence, sleep ensues. The cutting off of sensorial impressions aids in lessening the power of the attention and thus predisposes to sleep. Stillness, darkness, the absence of any decided impression on the skin, and the nonexistence of odors and flavors, accomplish this end. In these respects, however, habit exercises great influence, and thus individuals, for instance, who are accustomed to continual loud noises, cannot sleep when the sound is interrupted. As we have already seen, however, the predisposition to sleep is, in healthy persons, generally so great that when it has been long resisted, no sensation, however strong it may be, can withstand its power. _Digestion_ leads to sleep by drawing upon the brain for a portion of its blood. It is for this reason that we feel sleepy after the ingestion of a hearty dinner. A lady of my acquaintance is obliged to sleep a little after each meal. The desire to do so is irresistible; her face becomes pale; her extremities cold; and she sinks into a quiet slumber, which lasts fifteen or twenty minutes. In this lady the amount of blood is not sufficient for the due performance of all the operations of the economy. The digestive organs imperatively require an increased quantity, and the flow takes place from the brain; it being the organ with her which can best spare this fluid. As a rule, persons who eat largely, and have good digestive powers, sleep a great deal, and many persons are unable to sleep at night till they have eaten a substantial supper. The lower animals generally sleep after feeding, especially if the meal has been large. _Excessive loss of blood_ produces sleep. We can very readily understand why this should be so if we adopt the theory which has been supported in the foregoing pages. It would be exceedingly difficult to explain the fact upon any other hypothesis. I have seen many instances of somnolency due to this cause. It acts not only by directly lessening the quantity of blood in the brain, but also by so enfeebling the heart’s action as to prevent a due supply of blood being sent to the cerebral vessels.