A severely logical reference to previous doctrines regarding the condition of the brain during sleep, has led many authors to consider the therapeutical treatment of insomnia chiefly as a matter of modification of the cerebral circulation. Sleep has been supposed to depend upon a comparatively bloodless state of the brain, and wakefulness upon the contrary state. For such theorists the treatment of insomnia consists very simply in the use of agents which are supposed to be efficacious in reducing the flow of blood through the head. Tourniquets, placed upon the carotid arteries, occupy a position of great honor in the _armamentarium_ of such people. Recognizing the fact that changes in the force of the circulation accompany and sustain every change in the activity of the cerebral cortex, we, however, attach the greatest importance to the condition of the nervous substance itself. For a clear understanding of the proper mode of medication, it is important to ascertain whether the cerebral substance is in a state of normal activity, or whether it is in a state of healthy, but excessive, activity, or whether its seeming excitement is merely the result of irritable weakness. Since these opposite conditions may declare themselves during the course of any disease in which insomnia may become a troublesome phenomenon, it is impossible to make a classification of diseases upon the basis of these different states of the brain. It will, therefore, be found more useful to consider the subject of sleeplessness as it ordinarily presents itself during the clinical progress of the several forms of disease. It will, then, appear that the type of insomnia is liable to variation with the course of each individual malady; and its treatment must vary accordingly. Before proceeding to a discussion of the therapeutics of insomnia in connection with particular diseases, it will be advantageous to pass briefly in review the different remedies which are useful in the treatment of wakefulness. These may be divided into two classes: Nervous stimulants, and nervous sedatives. Among the first may be also reckoned food, heat, baths, and counter-irritants. Like all nervous stimulants, they promote the complete and harmonious action of all parts of the nervous system, favoring that equilibrium of the circulation which is most favorable to the development of sleep. The second class of agents comprises all such remedies as act directly upon the nervous tissue of the brain, depressing its functional activity, and hushing to rest those particular organs which, by their undue excitement, serve to keep the remainder in a state of wakefulness. All these substances produce decided effects upon the spinal cord and the peripheral nerves, but it is their operation upon the brain which principally interests us in connection with insomnia. NERVOUS STIMULANTS.