The onset of insanity may be gradual or sudden. More commonly the onset is gradual, and manifested by alterations of emotion and conduct, which may for a considerable period precede any impairment of intelligence. Periods of depression may alternate with periods of excitement. Irritability and instability of temper manifest themselves, and lead relatives and friends to become suspicious of the change that is the herald of serious mental impairment. Lack of interest in environment, business, or the usual pleasurable pursuits, also a tendency to personal seclusion manifest themselves, and changeability of the affections, more often to those nearly related, are not uncommon. Sooner or later the capacity to conduct business and allied pursuits becomes enfeebled, and the power of judgment lessened; depression begets apprehension and a dread of impending ruin in this world or in the world to come. Marked indecision and vacillation of action is quite common. Delusions follow, mostly of persecution, in the form of attempts to cause ruin or poisoning. Delusions associated with the special senses are common, particularly of hearing, supposed voices urging the committal of certain actions, or expressive of derision; of vision, by which objects are seen which are non-existent; of taste, imparting the idea of poisoning; of touch and pain, invoking peculiar sensations; of smell, conveying the idea that food, the body, &c., exhale disgusting odours. Associated with the onset of insanity, and remaining permanently, are three special distortions of perceptions--viz. _illusions_, _hallucinations_, and _delusions_. So long as the first two can be reasoned upon and rejected, judgment remains. At one or other time the afflicted person becomes so affected by them that they become realities, and are accepted as true and existent; then the judgment is perverted, and the person is said to suffer from a delusion. _Illusions._--An illusion is a false perception, a perversion of the senses, a mockery, false show, counterfeit appearance. The false perception is, however, invoked by some external appearance. _Hallucinations._--Hallucinations are perverted sensations and perceptions, for the production of which no external impulse is present. The person may complain of seeing horrible reptiles around, which are not present. So long as the reasoning faculties are capable of dispelling the alleged reality of the hallucination and rejecting it, it remains but an hallucination. If, however, it becomes accepted as a reality and the person becomes obsessed thereby, it becomes a delusion. _Delusions._--A delusion is a chimerical thought, an affection of the mind. It implies a disordered intellect. Delusions generally concern the insane person, his power, soul, &c. A delusion is a perverted idea of the mind in which there is belief in non-existent things or occurrences. Delusions may be based upon previous hallucinations, or arise out of erroneous conceptions. MANIA