Definition: is not surprising that many scientific and philosophical men have vainly exhausted their observation and ingenuity to find out some special quality, some peculiar mark or characteristic common to all cases of lunacy, which might serve at least as a guide in deciding on its absence or presence in individual instances. Being hopeless of a definition, they would willingly have contented themselves with a test, but even this the obscurity and difficulty of the subject seem to forbid.
5. Lord Erskine, who, in his practice at the bar, had his attention drawn this way, from being engaged in some of the most remarkable trials of his time involving questions of lunacy, has given as his test, "a delusive image, the inseparable companion of real insanity," (Ersk. Misc. Speeches) and Dr. Haslam, whose opportunities of observation have surpassed most other persons, has proposed nearly the same, by saying that "false belief is the essence of insanity." (Haslam on Insanity.) Sir John Nicholl, in his admirable judgment in the case of Dew v. Clark, thus expresses himself: "The true criterion is, where there is delusion of mind there is insanity; that is, when persons believe things to exist, which exist only, or at least, in that degree exist only in their own imagimation, and of the non-existence of which neither argment nor proof can convince them; they are of unsound mind; or as one of the counsel accurately expressed it, it is only the belief of facts, which no rational person could have believed, that is insane delusion." (Report by Haggard, p. 7.) Useful as these several remarks are, they are not absolutely true. It is indeed beyond all question that the great majority of lunatics indulge in some "delusive image," entertain some "false belief." They assume the existence of things or persons which do not exist, and so yield to a delusive image, or they come to wrong conclusions about persons and things which do exist, and so fall into a false belief. But there is a class of cases where lunacy is the result of exclusive indulgence in particular trains of thought or feeling, where these tests are sometimes wholly wanting, and yet where the entire absorption of the faculties in one pedominant idea, the devotion of all the bodily and mental powers to one useless or injurious purpose, prove that the mind has lost its equilibrium. With some passions, indeed, such as self-esteem and fear, what was at first an engrossing sentiment, will often go on to a positive delusion; the self-adoring egotist grows to fancy himself a sovereign or a deity; the timid valetudinarian becomes the prey of imaginary diseases, the victim of unreal persecutions. But with many other passions, such as desire, avarice or revenge, the neglect and forgetfulness of all things save one, the insensibility to all restraints of reason, morality, or prudence, often proceed to such an extent as to justify holding an individual as a lunatic, incapable of all self-restraint, although, strictly speaking, not possessed by any delusive image or false belief. Much less do these tests apply to many cases of irresistible propensity to acts wholly irrational, such as to murder or to steal without the smallest assignable motive, which, rare as they are, certainly occur from time to time, and cannot but be held as an example of at least partial and temporary lunacy. It is to cases where no false belief or image can be detected, that the remark of Lord Erskine is more particularly applicable; "they frequently mock the wisdom of the wisest in judicial trials," (Ersk. Misc. Speeches,) and were not the paramount object of all legal punishment the benefit of the community, which makes it inexpedient to spare offenders against the law, if insanity be the ground of their de-fence, except upon the clearest proof, lest skilful dissemblers should thereby be led to hope for impunity, very subtle questions might no doubt be raised as to the degree of moral responsibility and mental sanity attaching to the perpetrators of many atrocious acts, seeing that they often commit them tinder temptations quite inadequate to allure men of common prudence, or under passions so violent as to suspend altogether the operations of reason or free will. For as it is impossible to obtain an accurate definition of lunacy, so it is manifestly so, to draw the line correctly between it and its opposite rationality, or, to borrow the words of Chief Justice Hale, (1 Hale s P. C. p. 30,) "Doubtless most persons that are felons, of themselves and others, are under a degree of partial insanity when they commit those offences. It is very difficult to define the indivisible line that divides perfect and partial, insanity; but it must rest on circumstances duly to be weighed and considered both by the judge and jury, lest on one side there be a kind of inhumanity towards the defects of human nature, or on the other side too great an indulgence given to great crimes."
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