Two centuries ago, while modern medical science was still young, medical practitioners proceeded upon two general assumptions: one as to the cause of disease, the other as to its treatment. As to the cause of disease,—disease was sent by the inscrutable will of God. No man could fathom that will, nor its arbitrary operation. As to the treatment of disease, there were believed to be a few remedial agents of universal efficacy. Calomel and blood-letting, for example, were two of the principal ones. A larger or smaller dose of calomel, a greater or less quantity of bloodletting,—this blindly indiscriminate mode of treatment was regarded as orthodox for all common varieties of ailment. And so his calomel pill and his bloodletting lancet were carried everywhere with him by the doctor. Nowadays, all this is past, in medical science. As to the causes of disease, we know that they are facts of nature,—various, but distinguishable by diagnosis and research, and more or less capable of prevention or control or counter-action. As to the treatment, we now know that there are various specific modes of treatment for specific causes or symptoms, and that the treatment must be adapted to the cause. In short, the individualization of disease, in cause and in treatment, is the dominant truth of modern medical science. The same truth is now known about crime; but the understanding and the application of it are just opening upon us. The old and still dominant thought is, as to cause, that a crime is caused by the inscrutable moral free will of the human being, doing or not doing the crime, just as it pleases; absolutely free in advance, at any moment of time, to choose or not to choose the criminal act, and therefore in itself the sole and ultimate cause of crime. As to treatment, there still are just two traditional measures, used in varying doses for all kinds of crime and all kinds of persons,—jail, or a fine (for death is now employed in rare cases only). But modern science, here as in medicine, recognizes that crime also (like disease) has natural causes. It need not be asserted for one moment that crime is a disease. But it does have natural causes,—that is, circumstances which work to produce it in a given case. And as to treatment, modern science recognizes that penal or remedial treatment cannot possibly be indiscriminate and machine-like, but must be adapted to the causes, and to the man as affected by those causes. Common sense and logic alike require, inevitably, that the moment we predicate a specific cause for an undesirable effect, the remedial treatment must be specifically adapted to that cause. Thus the great truth of the present and the future, for criminal science, is the individualization of penal treatment,—for that man, and for the cause of that man’s crime.