_Delusions_ are false beliefs. We think a belief in the religion of Mahomet is a delusion, but not an insane one. Insane delusions arise from disease of the brain, and are a part of those mental changes that appear during its progress. The king, who, under the influence of disease, thinks himself a pauper and that he and his family are starving, and the pauper, who thinks himself a king, with all the wealth and power of one, have each insane delusions. Some delusions are fleeting and changeable, lasting a few days, weeks, or months, while others are fixed, lasting a lifetime; some are impossible and beyond rational belief, as when a man thinks himself Queen Victoria, or that his head is made of brass, or that he is dead, and yet sleeps and eats and talks; other delusions are possible, as when a king thinks himself a pauper, because such a thing may and even has happened, or when a pauper thinks himself a king, because people of very low degree have risen to such a station, but they are very improbable, and we do not expect such things among Americans, much less among our patients. Other delusions are not only possible, but relate to things that may or do happen, or are within the bounds of a rational belief, as that of a person who insists he has a cancer, or that he has committed the unpardonable sin, or that poverty is impending and the poorhouse not far off; or that of a woman that she has been violated, or that, when her child was sick she so neglected it, that it died. Such beliefs as these are delusions, when they have no other reason for their existence than that they are caused by disease. Some delusions are called homicidal, suicidal, or dangerous, because they cause a patient to do, or want to do, acts that are dangerous to himself or others, or property. _Hallucinations._--When a patient has hallucinations, he thinks he sees, hears, smells, tastes, or feels something, when there is really nothing to cause the sensations or ideas except diseased action of the brain; nothing being sent to the brain from any special organ of sense, he really sees, hears, smells, tastes, or feels nothing, it is all imagination, though seemingly very real. For instance, a person thinks he hears a voice, perhaps that of God, or of some one who is dead, or of an absent friend, or thinks he sees these persons, when there is nothing external to the brain to excite the sensation or give the idea.