Patients have not unfrequently laboured under the impression of their having taken poison, when there can never have existed the least ground for such a suspicion, and yet their general conduct has been in complete opposition to the idea of insanity:[1] a curious case of this kind is related in the _Sepulchretum_ of Bonetus; and even during the progress of the present work, the author was consulted upon an illness, which the patient seriously attributed to the operation of a slow poison, declaring that it had been secretly administered during a philanthropic visit to one of our public prisons. _Dr. Esquirol_[2] also relates the case of a lady, twenty-seven years of age, who in the last stage of phthisis pulmonalis perceived in her room the odour of burning charcoal, and immediately conceived that there was a design against her life; in consequence of which she left her lodging, and sought another abode, but the fumes incessantly pursued her, and she died fully convinced that she was the victim of some malicious persecution. But of all the fallacies with which we have to contend, no one is more dangerous in its effects, or more frequent in its occurrence, than that which leads them to mistake the identity of the offender; we have already alluded to this fallacy (_vol._ i. _p._ 440), and we shall hereafter have occasion to refer to it. When a medical practitioner is summoned to investigate a case, in which severe sufferings have supervened, without any apparent or assignable cause, the following interrogatories are calculated to elicit data for a just conclusion. _Previous state of the patient, with respect to bodily health and strength?_—The knowledge of these facts will materially assist us, not only in explaining the violence of the present symptoms, but in estimating their indications, in forming some opinion with regard to their causes, and in prognosticating their results. _The age and occupation_ are also to be ascertained. Violent tormina of the bowels, and other symptoms resembling those of acute poisoning, are frequently explained at once, by learning that the individual in question has been engaged in some trade or manufactory, from which he has been necessarily exposed to metallic exhalations; thus painters, gilders, smelters, and others, from living almost constantly in an atmosphere charged with such fumes, are always liable to sudden and violent attacks, dreadful cholics, paralysis, and premature death. _See our chapter on the poison of Lead, vol. 2, p. 336, and that on Aerial Poisons, page 457._