When, in 1810, Franz Joseph Gall said: "The measure of culpability and the measure of punishment can not be determined by a study of the illegal act, but only by a study of the individual committing it," he expressed an idea which has, in late years, come to be regarded as a trite truism. This called forth as an unavoidable consequence a more lively interest on the part of various social agencies in the personality of the criminal, with the resultant gradually increasing conviction that the suppression of crime is not primarily a legal question, but is rather a problem for the physician, sociologist, and economist. Whatever light has been thrown in recent years upon this most important social problem, criminality, did not issue from a contemplation of the abstract and more or less sterile theses on crime and punishment as reflected in current works on criminal law and procedure, but was the result of research carried on at the hands of the physician, especially the psychopathologist, sociologist, and economist. The slogan of the modern criminologist is, "intensive study of the individual delinquent from all angles and points of view", rather than mere insistence upon the precise application of a definite kind of punishment to a definite crime as outlined by statute. Indeed, the whole idea of punishment is giving way to the idea of correction and reformation. This radical change of tendency cannot be looked upon as a mere misdirected sentimentality on the part of modern society, but is the inevitable result of the final conviction that the solely punitive criminology upon which society has been relying in its efforts to eradicate criminal behavior from its midst has proved a total failure. The idea of punishment as a deterrent of crime is, as a consequence, gradually losing its hold upon modern criminologists, and in its stead we have been experimenting for some time past with such measures as probation, suspended or indeterminate sentence, and parole. Now it can not be too strongly emphasized that in giving these measures a fair trial we ought to guard against those very same grave errors which were chiefly responsible for the failure of the old, solely punitive methods, namely, the dealing with the criminal act rather than with the individual committing it. If these new measures of probation, suspended sentence, and parole, which are perfectly adequate in theory, are to justify their existence in the practical everyday handling of the problem of criminology, we must not fail to take into full account the very obvious natural phenomenon that human beings vary within very wide limits in their susceptibility to correction or reformation, that some individuals because of their psychological make-up, either qualitative or quantitative, are absolutely and permanently incorrigible and present a problem which can be dealt with in only one effective way--namely, permanent segregation and isolation from society. It is on this very