I have observed that the causes of trance are for the most part mental impressions; but it will be found that certain physical influences may produce the same results. The causes of trance, whether mental or physical, deserve again to be regarded in three lights. Either they have operated blindly and fortuitously, or they have been resorted to and used as agents to produce some vague and imperfectly understood result, or they have been skilfully and intelligently directed to bring out the exact phenomena which have followed. It is with trance supervening in the two former ways that I alone propose at present to deal; that is to say, with trance as it was imperfectly known as an agent in superstition, or as a rare and marvellous form of nervous disease. Of the third case of trance, as it may be artificially induced, I shall afterwards and finally speak. LETTER VI. TRANCE-SLEEP—The phenomena of trance divided into those of trance-sleep, and those of trance-waking—Trance-sleep presents three forms; trance-waking two. The three forms of trance-sleep described: viz., death-trance, trance-coma, simple or initiatory trance. Trance, then, it appears, is a peculiar mental seizure liable to supervene in persons of an irritable nervous system, either after mental excitement or in deranged bodily health. The seizure may last for a few hours, or a few days, or for weeks, or years; and is liable to recur at regular or irregular intervals. Trance again, it has been observed, has phases corresponding with the sleeping and waking of our natural state. And as natural sleep presents three varieties—the profound and heavy sleep of extreme exhaustion, ordinary deep sleep, and the light slumber of the wakeful and the anxious, so trance-sleep is three-fold likewise. But as in trance every thing is magnified, the differences between the three states are greater, and the phenomena of each more bold and striking. Two conditions are common, however, to every phase of trance-sleep; these are, the occurrence of complete insensibility, and that of vivid and coherent dreams. The insensibility is so absolute that the most powerful stimulants are insufficient to rouse the patient. An electric shock, a surgical operation, the amputation even of a limb, are seemingly unfelt.