The phenomena of reverie are similar in some respects to those of somnambulism. In this condition the mind pursues a train of reasoning often of the most fanciful character, but yet so abstract and intense, that though actions may be performed by the body, they have no relation with the current of thought, but are essentially automatic, and made in obedience to sensorial impressions which are not perceived by the brain. Thus a person in a state of reverie will answer questions, obey commands involving a good deal of muscular action, and perform other complex acts, without disturbing the connection of his ideas. When the state of mental occupation has disappeared, there is no recollection of the acts which may have been performed. Memory resides in the brain and can only take cognizance of those things which make an impression on the mind, or of those ideas which originate in the encephalon. In the case of a person performing on a piano, and at the same time carrying on a conversation, we have a most striking illustration of the diverse though harmonious action of the brain and spinal cord. Here the mind is engaged with ideas, and the spinal cord directs the manipulations necessary to the proper rendering of the musical composition. A person who is not proficient in the use of this instrument, cannot at the same time play and converse with ease, because the spinal cord has not yet acquired a sufficient degree of automatism, and the mind cannot be divided in its action. Darwin gives a very striking example of the independent action of the brain and spinal cord. A young lady was playing on the piano a very difficult musical composition, which she performed with great skill and care, though she was observed to be agitated and preoccupied. When she had finished, she burst into tears. She had been intently watching the death-struggles of a favorite bird. Though her brain was thus absorbed, the spinal cord had not been diverted from the office of carrying on the muscular and automatic actions required by her musical performance. The brain cannot entertain two ideas or initiate two acts at the same time. A person cannot, for example, think of a lamp and a book simultaneously; the thought of the one and the thought of the other will be found to alternate by any one who feels inclined to make the experiment, and not to exist at the same time. Neither can the brain think and simultaneously will. Whatever volitional acts it performs, are distinct from thought, and clearly separated from it by the element of time.