It would neither be possible nor profitable to refer at greater length to views which positive physiology has overturned. Observation and experiment have aided us greatly in arriving at definite conclusions on this subject, and the instances quoted on page 30 of this treatise, even if standing alone uncontradicted, would go far toward guiding us in the right path. On page 37 I have referred to the case of a man who, some time after receiving a severe injury of the head by which a considerable portion of the skull was lost, came under my professional care. Standing by his bedside one evening, just after he had gone to sleep, I observed the scalp slightly rise from the chasm in which it was deeply depressed. I was sure he was going to awake, but he did not, and very soon he became restless and agitated, while continuing to sleep. Presently he began to talk, and it was evident that he was dreaming. In a few minutes the scalp sank down to its ordinary level when he was asleep, and he became quiet. I called his wife’s attention to the circumstance, and desired her to observe this condition thereafter when he slept. She subsequently informed me that she could always tell when he was dreaming from the appearance of the scalp. My opinion, therefore, is that dreams are directly caused by an increased activity of the cerebral circulation over that which exists in profound sleep. This activity is probably sometimes local and at others general, and never equals that which prevails in the condition of wakefulness, when the functions of the brain are at their maximum of energy. This view is further supported by a consideration of the state of the brain in sleep and wakefulness, the condition of dreaming being, in a measure, an intermediate one. Illustrations of the effects produced by a notable increase in the quantity of blood circulating through the brain will be given in the chapter on wakefulness. All of these, it will be perceived, have a direct bearing on the question now under consideration. CHAPTER VI. MORBID DREAMS. Morbid or pathological dreams are divided by Macario[85] into three classes: the prodromic, or those which precede diseases; the symptomatic, or those which occur in the course of diseases; and the essential, or those which constitute the main features of diseases. As this classification is natural and simple, I propose to follow it in the remarks I shall have to make on the subject. PRODROMIC DREAMS.--There appears to be no doubt that diseases are sometimes preceded by dreams which indicate with more or less exactitude the character of the approaching morbid condition. Many instances of the kind which have been reported--especially by the earlier authors--are, however, in all probability merely coincidences; and in others the relation between the character of the dream and that of the disease is by no means clear.