This explanation applies _mutatis mutandis_ to all prodromic dreams. They are invariably based upon actual sensations, unless we except the rare cases which are simply coincidences. SYMPTOMATIC DREAMS.--Morbid dreams are so generally met with in the course of disease, especially in that of the brain and nervous system, that I never examine a patient without questioning him closely on this point. The information thus obtained is always valuable, and sometimes constitutes the most important feature of the investigation. _Fevers_ are very often accompanied by frightful dreams. According to Moreau (de la Sarthe),[96] their occurrence indicates that the attack will be long, and that there is probably some organic affection present. My own experience agrees with that of Macario,[97] to the effect of not confirming these opinions. I have, however, generally observed that the frequency and intensity of the morbid dreams were in proportion to the severity of the fever. _Diseases of the heart_ are very generally attended with disagreeable dreams. They are usually short, and, as Macario remarks, relate to approaching death. The patient starts from sleep in terror, and sometimes it is difficult to convince him of the reality of his visions. _Dyspepsia and other diseases of the intestinal canal_ often give rise to morbid dreams. They are usually accompanied by a sense of impending suffocation, and ordinarily consist of frightful images, such as devils, demons, strange animals and the like. The presence of worms in the intestines is likewise a frequent cause of such dreams. In _chlorosis_ dreams are very common. Occasionally they are of a pleasant character, but in the majority of cases they are the reverse of this. It would be difficult to mention a disease which is not, at some time or other of its career, an exciting cause of morbid dreams. The most interesting examples, however, are met with in cases of _insanity and other cerebral affections_, and frequently the delusions of the dreams are so mixed up with those which arise during the waking condition, that the patient is unable to separate them and to determine which are the consequence of erroneous sensations received when awake, and which are the results of dreams. The careful examination of almost any insane persons will also show that they incorporate the fancies of their dreams with the realities of everyday life. Indeed, the relations of dreaming to insanity are so interesting and important as to have attracted the marked attention of alienists and psychologists.