These may be classified under two general groups. First, those occurring as a result of peripheral stimulation of the senses, and second, those which are the products of mental association. These two sets of causes may occur separately or together. Example: A dream resulting from peripheral stimulation of the nerves. Persons frequently dream of being in a snow-storm when a portion of the body is exposed during sleep. The phenomenon to be noticed here, is that dreams magnify the sensations carried to the brain. In this we have a possible resemblance to the exaggeration produced upon the hypnotized subject by the suggestion of the operator.

Example of the second class of causes: Memory provoked by no discoverable cause may bring back long-forgotten events of childhood, and group them about with all sorts of fantastic imagery. Diseased states of the body may provoke exaggerated imagery while sleeping, and in dreams our personality may be changed.

Dr. Moll cites the experience of an officer who greatly admired the achievements of Hannibal. In a dream one night he thought he was Hannibal and conducted a dream warfare, crossing the Alps with his army, and fighting again in fancy the great battles which Hannibal had fought centuries before.

There are some differences between the phenomena of deep hypnosis and those of natural sleep. In deep hypnosis the suggestion of the hypnotist is logically fitted to the ideas in the mini of the subject. In the state of deep hypnosis the hypnotist can carry on a conversation with the one hypnotized. However, certain sleeping persons will converse with a person in the room if care and tact be used by the one awake. Secrets have been elicited in this way.

The hypnotized subject will imitate the movements of the operator. This is also true within certain very narrow limits of persons sleeping naturally. A person while sleeping will turn in bed and execute some simple command, but if it is long continued the sleeper will generally awake.