On those occasions where the madman has been tried in a criminal court, the counsel for the prosecution has usually and gravely enquired of the medical evidence, whether the prisoner on ordinary topics and on subjects unconnected with his insanity, would not converse in a rational manner: and also whether he did not possess sufficient understanding to discriminate between GOOD and EVIL, RIGHT and WRONG? When a medical person is employed concerning any one to whom insanity is imputed, his principal enquiry is concerning his _in_sanity: it is not his object to ascertain how much reason he possesses, but how far, and on what topics he is insane. And having gauged his insanity he has performed his duty. If it should be presumed that any medical practitioner is able to penetrate into the recesses of a lunatic’s mind, at the moment he committed an outrage; to view the internal play of obtruding thoughts, and contending motives—and to depose that he knew the GOOD and EVIL, RIGHT and WRONG he was about to commit, it must be confessed that such knowledge is beyond the limits of our attainment. It is sufficient for the medical practitioner to know that his mind is deranged, and that such state of insanity will be sufficient to account for the irregularity of his actions; and that in a sound mind, the same conduct would be deemed criminal. If violence be inflicted by such person during a paroxysm of rage, there is no acuteness of metaphysical investigation which can trace the succession of his thoughts, and the impulses by which he is goaded for the accomplishment of his purpose. And it will be shewn hereafter that in some instances he is not himself conscious of his actions. Should an equal injury be inflicted by the crafty and deliberate machinations of systematic insanity, where the motives to action are delusions, the scrutiny into the exact procession of thought which produced the motive, or excited the determination is likewise beyond the reach of the medical practitioner. As it would be difficult in a person of the soundest mind to detect the succession of thoughts, tracing that which was most remote _from_, to that which was proximate _to_, the action; it can less be expected that the medical evidence should be capable of noting the consecutive irregularities of a disordered intellect.