Disease, in the great majority of its forms, consists, according to the most scientific pathologists, in either an excess or deficiency of those transformative processes by which new structures are built up and the old dissolved and carried away, and on the continuance of which the healthy growth and sustenance of the organism depend. Until an animal is full grown the constructive processes are in their maximum state of normal activity; while, relatively, the destructive processes are at their maximum of abeyance. But for the continuance of healthy adult life the balance of organic change must remain always even: growth must be equalled by decay; the agents of each must do equal work. If after the attainment of maturity the relative activity of the composing and decomposing processes should continue the same as before in any part of the organism, hypertrophy or abnormal growth would be the result. If, on the other hand, that relative activity is reversed–the destructive metamorphoses becoming predominant, either locally or generally–there is corresponding atrophy. Moreover, as one of the essential conditions of normal life, the co-ordinate action of the constructive and destructive agencies must range, within certain degrees of rapidity, beyond those limits in either direction the regions of disease are entered on. If that action be unduly slow, the physical frame is weak, the emotional nature is apathetic, the intellect lacks energy–systematic thinking being a toilsome or impossible task; if successively slower still, corresponding phases of vital degradation are passed through, until at length death itself ensues. If, on the contrary, the transformative processes be unduly rapid, there is exuberance of activity, both muscular and mental: repose is suffering; the feelings are intense, but quickly changeable; the intellect exhibits an excess of energy– ideas too rapidly formed to admit of adequate development chase each other through the mind in quick succession, and, having no stability, fail to become effective forces, shaping the life of the individual to some great or definite end. The physical and mental calm of conscious strength which the most healthy natures experience is wanting, existence being impulsive, restless, tumultuous, feverish– a sort of border land between normal activity and the most temperate zones of inflammation.