In various diseases the nature and the period of the invasion of dreams afford a valuable ground of observation to the physician both in his diagnosis and prognosis of the case. In incipient hydro-thorax, for instance, dreams occur at the very moment the patient falls asleep, and he fancies himself suffocated by some impending and destructive weight. Diseases of the heart are accompanied by alarming dreams, from which the patient starts up in great terror. In children the perturbation of their sleep frequently indicates the seat of their sufferings; and the valuable researches on the nervous system by Charles Bell have enabled the medical attendant to read in the features of a sleeping infant whether the malady be in the head, the cavity of the chest, or the abdomen. If proof were wanting that dreams arise from our waking thoughts, it might be found in the circumstance of those sleepers who divulge their secrets, and verify the lines of Shakspeare: There are a kind of men so loose of soul, That in their sleep will mutter their affairs. Reason, therefore, prompts us to reject the idea of dreams being preternatural suggestions. In general, we may consider them as a morbid excitement of the brain, arising either from moral or physical causes, and depending essentially on the condition of our mind and body. Our most lively hopes are ever linked with fears that prey upon us even when most secure; and these apprehensions, recurring in our dreams, prove too often prophetic of the very events we dreaded. The prejudices of early education shed around these forewarnings circumstantial incidents; and fear is the greatest ally of superstition. If our visions by night are fraught with such singular circumstances, our "day dreams," or _reveries_, are frequently attended with strange associations. The impressions received during these ecstatic visions or trances will occasionally act so powerfully upon the mind, that during our waking hours and the usual pursuits of life we cannot divest ourselves of the existence of their reality.