of sleep, is evidence of a universal and uniform reduction of function throughout the body. Sleep seldom falls at once with equal force upon every organ; its invasion is progressive. Consequently, certain structures may be fast asleep, while others are partly awake,—while still other portions of the organism may be in a condition of activity greatly in excess of their ordinary wakeful function. Upon this fact depend the phenomena of dreams and the various forms of somnambulism. The special senses are usually overcome by sleep before the muscular apparatus yields, and the cerebro-spinal nervous centres are the last of all to succumb. The eyes, for example, cease to see clearly before the eyelids droop, or the muscles of the neck give way in the act of nodding. The senses of touch and of taste fail next in order, as in the case of the infant gourmand, who may be seen falling asleep at supper,—his mouth yet filled with untasted sweets from the table before him. The sense of smell is more persistent, and its exercise is sometimes an obstacle to the invasion of sleep. Witness the effect of powerful odors upon certain persons. The perfume of flowering plants in the sleeping chamber is sometimes decidedly annoying on this account. A lady of my acquaintance was once awakened out of a sound sleep by the smell of tobacco smoke from the pipe of a thoughtless burglar who had quietly entered a distant apartment of the house. A sudden change of wind, deluging a city with the vapors of a glue-factory or rendering establishment, may in like manner disturb the slumbers of thousands of people.

The sense of hearing seems to be the most persistent of all the special senses. It is not a very uncommon thing for persons to be awakened by the sound of their own snoring; or, if not actually aroused by the noise, to remain in a condition of repose which seems to be sustained and cheered by the regular rhythm of its own music. As a general rule, however, it is noteworthy that, when not wholly dormant, each sense finds its sphere of activity greatly narrowed by the fact of sleep. Consequently the range of perception, if not wholly obliterated, is greatly limited during the time of sleep.

While it is true that sleep arrests the voluntary activities of the muscles, it is also a fact that all the muscles do not yield at once or in equal degree. The extensors of the neck, and the supporters of the spinal column, are the first to fail. The patient begins to nod, and is inclined to fall forward, before consciousness ceases. The muscles of respiration and of circulation continue to contract, though at a diminished rate. The vermicular movements of the intestinal coats persist, and in certain conditions of ill-health their exaggerated contractions may become a cause of imperfect repose. Reflex movements may always be excited during natural sleep. Tickling the sole of the foot will cause retraction of the limb; and before the complete establishment of sleep, a certain exaltation of the spinal reflexes may be observed. Young children may frequently be seen in the act of suction with their lips, as if at the breast; and the smile of the sleeping infant is a matter of daily remark in every nursery. The influence of dreams as an excitant of muscular movement will be hereafter discussed.

The variation of intellectual function which appears in sleep serves to measure its profundity and to indicate the extent of its invasion. The act of perception being dependent upon sensation, it is to be observed that the range of perception diminishes so soon as the organs of sense begin to yield. Its intensity may not immediately fail, but the breadth of its scope is narrowed. Sometimes, however, the act of conscious perception is arrested before the organs of sense are sealed. The sleepy reader may continue to eye the page before him, perhaps even to read aloud for a considerable time after he has ceased to derive any meaning from the words of the book. In such cases the organs of perception and conception and association of ideas slumber before the bonds of connection between the will and the muscular organs have been completely relaxed. Such an example affords a valuable illustration of the division of the brain into separate mechanisms which, though most intimately related, are nevertheless partially independent of each other. Sleep may operate like an invasive disease, falling with unequal incidence upon the different structures that make up the mass of the brain, paralyzing one portion, while simply benumbing another, and even arousing to excessive activity a third. Consequently the intellectual functions may be very unequally disturbed, and the order of their subsidence may be considerably varied; but, as a general rule, the physiological relations of the faculties are respected, so that as sensation diminishes, perception fails, the conception of ideas is correspondingly hindered, and the association of such ideas as are still projected upon the field of consciousness becomes more imperfect. The loss of the power of association implies the destruction of memory and the impossibility of exercising the reasoning faculty or of forming those judgments upon which every act of volition is based. When the brain has at length been so far overwhelmed that physical impressions can no longer reach the field of consciousness, all manifestation of intellectual life is at an end, and the sleeper sleeps a dreamless sleep that leaves no trace behind.

It is assumed in the last sentence that the brain may become so far transformed by sleep that it ceases for the time to be capable of function as the instrument of thought. This conclusion has been questioned by the very highest authorities. Sir William Hamilton, Exner, and many others have instituted numerous experiments to test the possibility of a dreamless sleep. Causing themselves to be suddenly aroused at all hours of the night, they invariably found themselves at the instant of awaking occupied with the course of a dream. Hence it has been inferred that the mind is always alert, even when the body is most thoroughly asleep. In explanation of the fact that consciousness contains after deep sleep no trace of such mental activity, it is claimed that the act of dreaming of which we are aware at the moment of waking is proof of intellectual function during the moments which preceded that incident, and that we are merely forgetful of all similar processes that occurred during undisturbed sleep. The unconsciousness of sleep, according to this theory, is not real—it is only apparent through failure of the memory. If this be true, memory is the only intellectual faculty of whose inaction we can be sure. The period of deep sleep might then be, for all we know to the contrary, a period of the most intense and exalted mental activity. But, if so, it is quite worthless as a constituent of our conscious existence. It may also be objected with equal reason that the dreams which unquestionably occupy the field of consciousness at the instant of waking are probably excited by the impressions which terminate sleep. The process of waking, though often very greatly hurried, is by no means absolutely instantaneous. As we shall learn, the time requisite for the evolution of a dream may be indefinitely brief. Consequently, it seems better in all such instances to assign the period of dreaming to the time of diminishing slumber that corresponds to the disturbance by which sleep was terminated.

The only reason for any hesitation in the acceptance of such a proposition consists in the reluctance of many philosophers to admit the possibility of any interruption in the active life of a spiritual being, such as man is conceived to be. But it is difficult to comprehend any valid reason for the denial of such interruption. Every form of