is often used to discover whether madness be real or only feigned. Apoplexy, which consists of a turgid state of the cerebral vessels, produces perhaps the most complete sleep that is known, in so far that, while it continues, it is utterly impossible to waken the individual: no stimulus, however powerful, has any influence in arousing his dormant faculties. When, however, the cerebral determination is the result of acute disease, and does not go the length of oppressing the brain, sleep is prevented, and an accumulation of sensorial power takes place. This is seen in fevers and various other disorders.

The power of narcotics is hardly less remarkable. Their operation is a gradual one. At first a slight drowsiness comes on, succeeded by a complete suspension of the intellectual powers, and of the organs of the senses and voluntary motion. Thought, muscular movement, and sensation of every kind, are suspended. It is truly a complete slumber-no one faculty, save the vital organs, being in operation.

Full-bodied phlegmatic persons are naturally much better sleepers than others. This I conceive to proceed from two causes; 1st, from the greater pressure of blood on their brain; and 2d, from their natural dispositions being less airy, sensitive, and irritable than those of opposite temperaments. Their minds are usually of an obtuser cast, their

sensibilities less acute, and their susceptibility to impressions of all kinds of a far inferior description. They have more of the animal in their nature; and impressions which would operate with keen power upon finer spirits, produce no effect upon their impassive frames of mind.

Too feeble a cerebral circulation has precisely the same effect as the opposite state. Thus, excessive loss of blood excites sleep; and, generally speaking, there is less determination of blood to the brain in slumber than in the waking state.

A heavy meal, especially if the stomach is at the same time weak, is apt to induce sleep. In ordinary circumstances, the sensorial power residing within this viscus is sufficient to carry on its functions, but when an excess of food is thrown upon it, it is then unequal to furnish, from its own resources, the necessary powers of digestion. In such a case it draws upon the whole body-upon the chest, the limbs, &c. These parts supply it with the sensorial power of which it is deficient; and by their aid it is able to perform that which by its own unassisted means it never could have accomplished. But mark the consequences of this accommodation! The granters of the draft suffer by their own generosity; and by enabling the stomach to get out of difficulty, they get into it themselves. The extremities become

cold, the respiration heavy and stertorous, and the brain torpid. In consequence of the state of the latter organ, sleep ensues. It had parted with that portion of sensorial energy which kept it active and awake; and by supplying another viscus with the means of getting on, is thrown itself into a state of temporary weakness and oblivion.

When, therefore, the sensorial power which keeps our faculties in activity is exhausted, we naturally fall asleep. As the exhaustion of this power, however, is a gradual process, so is that of slumber. We glide insensibly into it, as from life into death; and while the mind remains poised, as it were, between sleep and the opposite condition, it is pervaded by a strange confusion which almost amounts to mild delirium: the ideas dissolve their connection from it one by one; those which remain longest behind are faint, visionary, and indistinct; and its own essence becomes so vague and diluted, that it melts away into the nothingness of slumber, as the morning vapours are blended with the surrounding air by the solar heat. Previous to the accession of sleep, a feeling of universal lassitude prevails. This sensation heralds in the phenomena of slumber, and exhibits itself in yawning, heaviness of the eyes, indifference to surrounding objects, and all the characteristics of fatigue. If the person be seated, his head nods and droops;

and, in all cases, the muscles become relaxed, and the limbs thrown into that state most favourable for complete muscular inaction. The lying position is, consequently, that best adapted for sleep, and the one which is intuitively adopted for the purpose. The organs of the senses do not relapse into simultaneous repose; but suspend their respective functions gradually and successively;-sight, taste, smell, hearing, and touch parting with sensation in the order in which they here stand, and gliding insensibly away. In the same manner, the muscles do not become simultaneously relaxed-those of the limbs giving way first, then those of the neck, and lastly the muscles of the spine. Nor do the external senses, on awaking, recover all at once their usual vigour. We, for some seconds, neither hear, nor see, nor smell, nor taste, nor touch with our usual acuteness. Ordinary sights dazzle our eyes; ordinary sounds confuse our ears; ordinary odours, tastes, and sensations, our nose, our tongue, and our touch. They awake successively, one after its fellow, and not in the same instant.

Sleep also produces important changes in other parts of the system. The rapidity of the circulation is diminished, and, as a necessary consequence, that of respiration; but the latter function does not part otherwise with any of its customary vigour; on the

contrary, it acquires an accession of energy, breathing being more full than in the waking state; the pulse also, though slower, is stronger. Animal heat is slightly reduced upon the surface, while digestion, absorption, and nutrition, all proceed with increased energy. On this account, sleep is the period in which the regeneration of the body chiefly takes place, and in which nourishment is most copiously infused into the blood. This law also governs the vegetable kingdom, the productions of which increase more during the night than at any other period of their existence. The intellectual and voluntary powers being dormant, is the obvious cause why some of the functions, and the stomach among others, acquire an increase of action, for the sensorial power which belongs to the former being withdrawn from them for a season, is directed to other channels. Were there even no augmentation of power given to the nutritive process at this period, the body would be more thoroughly strengthened than when awake, for all those actions which weaken it in the latter condition are at rest, and it remains in a state of quietude. If there be any parts in which the vigour of the vascular action is diminished, they are the brain and organs of volition. The activity of the former is increased by a vigorous flow of blood to it, and consequently when it is comparatively inert, as in sleep,