It is chiefly, however, in abnormal activity that the presence of this cerebral depreciation is indicated. And here we find the same disposition to insist on positive and absolute conditions, overlooking those nicer shades of diversity which mark the movements of Nature. It is the common belief that between eccentricity and insanity a great gulf is fixed; and in courts of justice this notion is often used with great effect to overthrow the conclusions of the medical expert, who, while he admits their essential difference, finds it not very easy to avoid the trap which a quick-witted lawyer is sure to make of it. Let him recognize the fact that they are the results of a common agency, differing chiefly in degree, and then his path is clear, though it may not lead to popular confidence in his professional views. Neither is the cerebral depreciation confined to any particular portion of the organ; and therefore its effects may be witnessed in any of those manifestations which are known to depend upon it. The affective powers, meaning thereby the passions, affections, and emotions, are, like the intellectual, connected with the brain, and, like them too, are shaped, in a great degree, by the quality of that organ. It is curious, however, that, while this fact is admitted in general terms, there is a prevalent reluctance to make the legitimate practical application. It is denied that the moral powers and propensities can be affected by disease, though connected with a material organ. Everybody believes that a man who thinks his legs are made of glass is insane; but if his affections only are disordered,--love and kindness being replaced by jealousy and hate,--an habitual regard for every moral propriety, by unbounded looseness of life and conversation,--the practice of the strictest virtue, by unblushing indulgence of crime, and all without apparent cause or motive,--then the morbid element in the case is overlooked and stoutly repudiated. We admit that a man may be a fool without any fault of his own; but if he fall short of any of the requirements of the moral law, he is regarded as a sinner, and perhaps punished as a criminal. Before we utterly condemn him for failing to recognize all the sharp distinctions between right and wrong, for yielding to temptation, and walking in evil courses, we are bound in justice to inquire whether a higher grade of moral excellence has not been debarred him by the defective quality of his brain, the organ by which all moral graces are manifested,--whether it has not become deteriorated by morbid predispositions, transmitted with steadily accumulating force, to insanity, or other affections which are known to spread their noxious influence over the nervous system.