The legislator should apply the rules of social hygiene in order to reach the roots of criminality. But this would require that he should bring his mind and will to bear daily on a legislative reform of individual and social life, in the field of economics and morals as well as in that of administration, politics, and intelligence. Instead of that, the legislators permit the microbes of criminality to develop their pathogenic powers in society. When crimes become manifest, the legislator knows no other remedy but imprisonment in order to punish an evil which he should have prevented. Unfortunately this scientific conviction is not yet rooted and potent in the minds of the legislators of most of the civilized countries, because they represent on an average the backward scientific convictions of one or two previous generations. The legislator who sits in parliament today was the university student of 30 years ago. With a few very rare exceptions he is supplied only with knowledge of outgrown scientific research. It is a historical law that the work of the legislator is always behind the science of his time. But nevertheless the scientist has the urgent duty to spread the conviction that hygiene is worth as much on the field of civilization as it is in medicine for the public health. This is the fundamental conviction at which the positive school arrives: That which has happened in medicine will happen in criminology. The great value of practical hygiene, especially of social hygiene, which is greater than that of individual hygiene, has been recognized after the marvelous scientific discoveries concerning the origin and primitive causes of the most dangerous diseases. So long as Pasteur and his disciples had not given to the world their discovery of the pathogenic microbes of all infectious diseases, such as typhoid fever, cholera, diphtheria, tuberculosis, etc, more or less absurd remedies were demanded of the science of medicine. I remember, for instance, that I was compelled in my youth, during an epidemic of cholera, to stay in a closed room, in which fumigation was carried on with substances irritating the bronchial tubes and lungs without killing the cholera microbes, as was proved later on. It was not until the real causes of those infectious diseases were discovered, that efficient remedies could be employed against them. An aqueduct given to a center of population like Naples is a better protection against cholera than drugs, even after the disease has taken root in the midst of the people of Naples. This is the modern lesson which we wish to teach in the field of criminology, a field which will always retain its repressive functions as an exceptional and ultimate refuge, because we do not believe that we shall succeed in eliminating all forms of criminality. Hence, if a crime manifests itself, repression may be employed as one of the remedies of criminology, but it should be the very last, not the exclusively