INSANITY AND ITS MEDICO-LEGAL ASPECTS 363 as a dangerous lunatic, and should be kept under proper restraint, for, owing to the delusions arising from these hallucinations, he may be incited to commit suicide or homicide. 3. Illusion.—An illusion is a false interpretation by the senses of an external object or stimulus, which has a real existence. For instance, a man may imagine a string hanging in his room to be a snake, or may, in the dark, mistake the stem of a tree on the roadside for a ghost. A sane man may experience illusions, but, by closer investigation and his judging power, he is capable of correcting the false impression. An insane person cannot do so. He believes the illusion to be a reality and bases his conduct on that assumption. An illusion by itself is not a sign of madness, but, owing to madness, the patient lacks the power or resolution to examine his illusion. Illusions of sight, hearing and other senses may occur in cases of mental disease. 4. Impulse.—This is "a sudden and irresistible force compelling a person to the conscious performance of some action without motive or forethought".1 Normally, when a man, intends to do any act, he tries to realize its consequence and then decides whether he should accomplish it or not. If he finds that the consequences are unfavourable, he can restrain himself and will not undertake that act. An insane man has no balance of mind to use the reasoning faculty, and commits the act as soon as the idea occurs to him. He has no power to control it, however bad the conse- quences may be. It is possible that he may repent of his action afterwards. The clinical types of irresistible impulses which are generally noted are kleptomania (an irresistible desire to steal articles of little value), pyro- mania (an irresistible impulse to set fire to things), mutUomania (an irresistible impulse to maim animals), dipsomania (an irresistible desire for drink at periodical intervals), sexual impulses which include all acts of sexual perversions and suicidal and homicidal impulses. Such impulses are commonly met with in cases of imbecility, dementia, acute mania and epileptic insanity. 5. Obsession.—By obsession is meant "an imperative idea constantly obtruding itself upon the consciousness in spite of ail efforts of the sufferer to drive it from his mindJ>.2 An obsessive idea arises from the emotional state, and the intellect protests against it. In fact it affords an excellent illustration of a border line between sanity and insanity. A man goes to bed at night after securely bolting the door of his room, but he immediately gets up to see if he has done so. If he repeats the process once or twice and then, being fully convinced of the security of his room, goes off to sleep, he is considered a sane person. On the contrary y if he does not sleep, and spends the whole night in frequently inspecting the security of the bolt, he is certainly to be considered insane, and requires to be placed under proper care and control. Obsessive ideas generally occur among persons suffering from brain fag or nervous exhaustion. Very often they are unpleasant and annoying to the patients, who may wish to drive them from their minds, but cannot do so. These ideas are not infrequently accompanied by some .sort of dread or fear. Overbeck-Wright mentions the case of a woman who had been well-to-do, but came down in life after her husband's death. She had a daughter. Both of them were living with some distant relatives. At night the mother and child occupied one room. Site was very much worried about the future of her daughter as slie had no moaey and gradually felt the desire come upon her to frill the child. Several times she asked her relatives to keep them separate, informing them of the reasons why she wished, so* they simply scoffed, and to emphasize their incredulity locked the mother smd 1. Overbeck-Wright, Lunacy m Indm, p, 12, S1 2. Ibid., p. 13.