When one has wearied himself, and his perceptions have been somewhat obscured, even though nothing had occurred of the nature of unconscious cerebration, it would not be surprising if after refreshing sleep the first effort of his mind should classify and complete the undigested work of the day before. The dream imagery under which such things are done frequently invests the operation with a mysterious aspect, which, on analysis, appears most natural. I am informed by one of the participants that some time since two gentlemen in Pennsylvania were conversing concerning an intricate mathematical problem. One of them succeeded in its solution by algebraic methods. The other insisted that it could be done by arithmetic, but, after making many efforts, gave up the problem, and retired for the night. In the morning he informed his friend that in the night, while he was asleep, an old Scotch schoolmaster, who had been his instructor many years before, appeared to him and said, "I am ashamed of you that you could not do that sum. It can be worked out by arithmetic, and I will show you how now." And he added that he had immediately done so, and in the morning when he awoke he had put the figures on paper just as his schoolmaster had done in the dream; and there they were, a complete solution of the example.

It was a very impressive dream, but easily explained. It was a workable problem. The man, ashamed of himself that he could not do it and exhausted with his efforts, had sunk into a troubled sleep. His mind undoubtedly bad recurred to his old teacher and the rule; and as he dreamed about the matter, the working out of the problem had to come in some form. What more natural than that the image of the teacher who taught him the greater part of what he knew of the subject of arithmetic, especially in difficult problems, should have come in to give bodily shape to the shame which he felt, and that his fancy should attribute the information to him? So that, instead of such a dream being extraordinary, it is the most natural method in which it could occur.

The mind when awake is capable, by an effort of the imagination, of conceiving most grotesque ideas. For example, a man sees before him a huge rock. He may conceive the idea that that rock is transformed into pure gold, and that upon it is a raised inscription, made of diamonds, promising the rock as a reward for the guessing of a conundrum. Being awake, he perceives both clearly—the rock in its original character, and the image of the gold rock with the raised letters in diamonds. Perceiving both, he knows the rock to be real and the other to be fantastic. If the faculties by which he identifies the granite rock were to be stupefied, leaving those by which he conceives the idea of the gold and diamonds in full exercise, it is clear that he would believe that the granite rock was gold. If awake, in this state, he would be insane; if asleep, he would be dreaming. So, if the dreamer be absorbed in images which seem to him real, if the faculties by which he would distinguish an ideal conception from an objective reality were restored, he would take cognizance of his surroundings, and though the image might remain it would not seem real. The statement of this self-evident fact is sufficient to show what all the evidence I have eollated combines to prove, that Mercutio, in " Romeo and Juliet," was scientifically correct when he said:

True, I talk of dreams, Which are the children of an idle brain, Begot of nothing but vain fantasy.

Nightmare, with all its horrors, is but a variety of dream. The causes for its peculiarities are various — position; pressure upon the stomach, whereby the sympathetic nerves are affected, and through them the brain; extreme fatigue, etc. When one is awake and has precisely the same unfavorable physical sensations which would produce nightmare, he refers them to their proper source, changes his position, measures the probable consequences, resorts to medical aid, or absorbs himself in work; but when asleep, the mind attempts to account for the sensation, and will perhaps construct an image of Bunker Hill Monument pressing upon his chest to account for a sensation which, if he were awake, he would have no difficulty in explaining.

The relation to nightmare of sleeping on the back is so simple as hardly to need an explanation. Many persons never have an attack unless they get into this position.

Somnambulism differs from dreams in the fact that one or more of the senses may be in an active condition, and that one or more of the organs may respond to the idea which absorbs the mind. A merchant in New York, traveling on the Mississippi River, occupied the same state-room with a stranger of highly respectable appearance. In the morning the stranger, taking up his stockings, said sadly, "I see I have been at my old tricks again." "To what do you refer?" asked the merchant. " My stockings are wet, and I must have arisen in the night and traveled all over the ship".

As already remarked, talking in the sleep is the simplest form in which somnambulism appears. Usually dreamers do not move their limbs, and especially are incapable of rising or walking, because under ordinary circumstances the impulse to do these things is created by the will, and it requires a strong exertion thereof to overcome the inertia of the body and to begin the complex series of motions necessary to move from place to place. In sleep the image is not sufficientlv vivid to take control of the muscles.

Cicero says that if it had been so ordered by nature that we should actually do in sleep all that we dream of doing, every man would have to be bound to the bed before going to sleep. The justice of this remark is illustrated in the case of somnambulism.

The peculiarity of somnambulism which identifies it with dreaming is complete absorption of all the powers and faculties in the image. A voice falling in with that may be heard; one speaking of other matters is unnoticed. Dreamers who have never been somnambulists could, by a process of training, be transformed into such ; and, what is more important, the tendency can be destroyed if taken in time.

Sir Henry Holland says that it is an old trick to put the hand into cold water, or to produce some other sensation not so active as to awaken, but sufficient to draw the mind from a more profound to a lighter slumber; thus the sleeper may be made to answer questions.

Great light has been reflected upon natural by artificial somnambulism, known by the various names of mesmerism, animal magnetism, electro-biology, hypnotism, etc. It is an astonishing fact that in these stales a particular sense may be exalted so as t<> give results which in a normal condition would be impossible; and which to a superficial observer, and. even to an investigator if he be inexperienced, appear to transcend the bounds of the human faculty. Abnormal states, involving changes radically different from dream somnambulism, happen spontaneously when awake, occur in delirium, and at rare intervals the somnambulist may pass into them. They will be treated elsewhere.