I fully believe that in time the study of the psychotic phenomena developing in criminals will give us a correct insight into the nature of the criminal personality and thus aid in the solution of that problem which baffles criminologists today. We know that while pure experimental psychology and psychopathology have aided us in understanding the human mind both in health and disease, we owe the bulk of our knowledge in this field to the investigations of Nature's phenomena and experiments. The human mind, the most complex and intricate organ, lends itself but very feebly to analysis when all its component parts work in unison, and it is only when through disease it has become, so to speak, disintegrated into its various units, that a more ready access to it becomes possible. This is being fully appreciated both by psychologists and psychopathologists. Mental medicine, however, if it is viewed from the present-day broad conception of the term, must not confine itself exclusively to psychotic manifestations in the strictest sense of the word, but should embrace within its realm that great mass of unfortunates who populate our prisons, poorhouses and reformatories. It is now being universally recognized that the pauper, the prostitute, and the criminal classes are primarily products of mental defect and degeneracy and as such must come within the purview of mental medicine. This being the case, the same truisms which apply to the insane in general must likewise apply to the above-mentioned types. We are here especially concerned with criminals who, because of a mental breakdown, have come under the observation of a psychiatrist, and if we agree with many eminent criminologists that the present juvenile state of this science and the ineffective methods of dealing with crime are due to a lack of proper scientific understanding of that anomalous species which is grouped under the term "criminal man", why not endeavor to solve this problem by approaching it from the psychiatric point of view. If the study of psychopathology has given us such valuable data concerning the normal mind, why not expect that a similar study applied to the insane criminal will bring to light some important facts concerning crime and the criminal in general. It is for this reason that that large group of mental disorders developing in criminals during imprisonment which has been included under the term "prison psychoses" is of special importance to the psychiatrist.