derangement, it may be only necessary that these microscopic cells should be temporarily deprived of their normal supply of oxygen through the vascular system; or, on the other hand, a slight increase in the supply of the proper nutriment or stimulus may cause the same results. A simple loss of equilibrium, or change of tension in the nerve-cell, may cause delirium. These abnormal physical conditions may be temporary or permanent, but in either case they will probably, in the future as in the past, elude the most careful observation of the physician, the chemist, and the microscopist. Science has calculated the vibrations of the musical chord, and measured the oscillations of a ray of light, but has not estimated the vibrations of the living intellectual nerve-cell, nor analyzed its aura which waits incessantly and instantly upon its will. It has furnished no means, therefore, of determining mathematically when the mysterious organ of the mind is out of tune, or why its notes are discordant.
2. Hitherto no one has furnished a definition of insanity which will cover all of the supposed examples. Nor, considering the nature of the subject, is it probable that it will ever be done. It may be easy to differentiate a certain class of cases. We can say, without fear of contradiction, that a raving and uncontrollable maniac is insane, or that another, whose life has been uniformly consistent and harmonious, is sane. But this is not the class of cases in reference to which our opinions are asked. They do not give rise to litigation or dispute. Our opinions are only asked when there exists some room for doubt as to the exact mental condition of the person in question, and who therefore occupies a position near the border-lines which separate insanity from sanity; but no legal or scientific authority has established these lines. They are not indicated by broad rivers, or mountain-ranges, such as form the natural boundaries between nations; but the opposite conditions here become insensibly merged, in such a manner that no one can say where one ends and the other begins. One might as well attempt to determine the exact limits of the auroral lights.
Says Ray, in his classical treatise on "Mental Pathology," "One source, and perhaps the principal, of the prevalent error, is the habit of regarding insanity as a sharply defined phenomenon, easily separated from all accompanying incidents, like an earthquake or a chemical action, instead of a condition arising from obscure beginnings, culminating more or less rapidly, and declining by imperceptible steps, as the darkness of night is succeeded by the light of common day." In these doubtful cases the expert has to consider the possible motives of the individual, his hereditary tendencies, his education, social influences, his previous habits, his condition as to health or disease, and a multitude of other matters, all of which are to be carefully weighed and balanced against each other, before he can form a correct judgment as to whether a certain act or line of conduct implies insanity and irresponsibility or not. That there should not be exact,
