This occasional display of rationality, although admitted by all who have had experience of the insane, excites a doubt in the minds even of learned and intelligent persons who have merely speculated on this disease. They have conceived, from the existing philosophy of the intellect, that reason is the directress of human actions,—that this high arbiter of thought is an undivided principle,—that where the rudder is attached the ship may be steered—and that he who reasons must be rational: and so he is, _as long_ as he _does_ reason. But the inference of the integrity of the reasoning faculty in consequence of occasional gleams, is a gratuitous and groundless supposition. It often happens that persons may converse for some time with a lunatic, and find him apparently composed and rational; he will discuss the floating topics of the day as another man,—accord with the most enlightened on the general principles of morals, and correctly estimate the light and shadow of human conduct. If the observer should here retire he might be convinced of his sanity: but let him protract the discourse, let him touch the fatal string which throws his mind into discord: let him draw the hair-trigger which inflames the combustible materials of his disease, and he will be surprised if not alarmed at the explosion. The sweeping tyranny of madness scorns the demarcation which limits the sober mind; and it should likewise be taken into account that the subjects which constitute the insanity of a person, are the prominent features of his mind, and are more frequently recurred to than any other. It is true he may discuss ordinary topics like other men; but this to him is a species of bye-play, and he soon reverts to the interest or catastrophe of his drama. Whatever may be the subject of discourse, and however rationally he may appear to treat it, the experienced practitioner will expect, and he will not often be disappointed, to find that by some unaccountable association, even ordinary topics are linked with his darling delusion,—the map of his mind will point out that the smallest rivulet flows into the great stream of his derangement.