Lemoine[70] begins his chapter “_On the State of the Mind during Sleep_” with the assertion that “there is no sleep for the mind.” He is obliged, however, to admit that “when the organs of the body are benumbed by sleep, the mind appears to be in a particular state; it seems to be submitted to other laws than those which govern it during wakefulness; it seems to have lost for a time its most precious faculties.” During sleep the mind is, as he supposes, in a particular state, for, as has been shown in the previous chapter, it has lost many of its chief parts. The laws which govern it are, however, the same which always regulate it. The body upon which their power is primarily exercised--the brain--is not in the same condition during sleep as during wakefulness, and hence the differences in the evidences of cerebral activity. Sir William Hamilton[71] is generally considered to have determined affirmatively the question of the continuance of the action of the brain during sleep. He caused himself to be aroused from sleep at intervals through the night, and invariably found that he was disturbed from a dream, the particulars of which he could always distinctly recollect. But a full knowledge of the subject he was investigating would have sufficed to convince Sir William that the conclusion he drew from his experiments was altogether fallacious. It is well known that dreams are excited by strong impressions made upon the senses, or by irritations arising in the internal organs. Thus Baron Trenck relates that when confined in his dungeon he suffered the pangs of hunger almost continually, and that his dreams at night were always of delicate meats and sumptuous repasts, spread before him on luxuriously-furnished tables. The mere excitation of waking a sleeping person is generally sufficient to give rise to a dream. Maury, in his very interesting work, to which reference has already been made, and which will hereafter be more specifically considered, adduces many examples of dreams produced by sensorial impressions. I have myself performed many experiments with reference to this point, and have generally found ample confirmation of Maury’s investigations. It may therefore, I think, be assumed, without any violence to the actual facts of the cases, that the brain is not always in action, and that there are times when we sleep without dreaming.