It has been very justly observed, that to constitute insanity it is not necessary to exhibit the ferocity of a wild beast, nor to perform the antics of a buffoon; the most ordinary observer can tell when a person is furiously mad,[530] but, in many cases, “_such thin partitions do the hounds divide_,” that all the skill and discernment of a medical practitioner is required to establish the fact of insanity. It is to such cases as are more likely to become subjects of legal investigation, that the following observations particularly apply. _Sir Matthew Hale_ says, “there is a _partial_ insanity, and a _total_ insanity; the former is either in respect to things, _quoad hoc vel illud insanine_, where persons are perfectly rational, except on some one particular subject.” This fact is universally admitted, constituting a form of mental alienation to which _M. Esquirol_[531] has bestowed the name of _Monomania_, and of which every work on insanity abounds with examples. It is in such cases that the value of medical sagacity and experience becomes apparent, and the full developement of the real state of the patient’s mind and opinions will, in some instances, require considerable time and patience. “It is nearly impossible,” says _Dr. Haslam_, “to give any specific directions for conducting such an examination as shall inevitably disclose the delusions existing in the mind of a crafty lunatic; but in my own opinion it is always to be accomplished, provided sufficient time be allowed, and the examiner be not interrupted. It is not to be effected by directly selecting the subjects of his delusion, for he will immediately perceive the drift of such enquiries, and endeavour to evade, or pretend to disown them; the purpose is more effectually answered by leading him to the origin of his distemper and tracing down the consecutive series of his actions and association of ideas; _in going over the road where he has stumbled, he will infallibly trip again_.” There is, says _Dr. Male_,[532] a madness which shews itself in words, and another in actions; a lunatic may be coherent in conversation, but insane in conduct; he may be rational when under the restraint of a mad-house, but when released, and at liberty to act according to the impulse of his hallucination, will shew by his conduct that he is really insane.