If one accepts the point of view that the cause of crime is to be considered analogous to that of pulmonary tuberculosis, his understanding of the etiology of crime gains immensely. The old question of whether the criminal is born or made is answered, “both.” But the emphasis from our present data is on the inborn tendencies. Moreover, being born with the criminal diathesis does not mean that a person is predestined to commit crime, but that he is more likely than his neighbor to be infected by the contagion of delinquency. We have only to catch the trend of recent scientific research to extend our vision further. The criminal does not lack a simple unit character which would otherwise make him whole as some of the disciples of Mendel seem to argue. Neither is the criminal diathesis a simple instinctive tendency like the tendency to make a specific response to a specific stimulus, _e. g._, to wink when an object approaches the eye; the criminal is not charged with a specific propensity to commit murder or to steal. The safety of those who are more susceptible lies in keeping away from the contagion of bad example and temptations to fall, toward which he is generally less resistant than others. Specific training in strengthening and guarding his weakest spots may in time build up a resistance to temptations, the amount of which we cannot yet measure. His hope lies in the recognition of his weakness and the adjustment of his living so that his whole organism may support the breach in his make-up during the struggle with himself and with society.