This Book is a commentary on my experiences as an official visitor of the Institutions for the Insane and the Charities and Reformatories of the State. Its intent and purpose are to illustrate with as few technicalities as possible the illusive nature of insanity, its origin in the derangement of the functions of the brain-cells, the extreme impressibility of these cells and our power to increase or repress their activities. In these facts, which modern science has developed, are found the scientific principles on which the prevention of insanity, and its successful treatment, must be based. The same principles are shown to be applicable to the education of the mentally defective classes and to the reform of criminals. This Book should prove helpful in the prevention of insanity at the different periods of life and hopeful of the time when biology shall be able to completely unfold the mysterious mechanism of the brain, physiology to explain the function of every nerve centre and psychology to interpret the significance of all mental phenomena. -THE AUTHOR.