But curative measures are important, also, in dealing with the criminal, and each distinct class must be dealt with differently. We noted in the beginning of the chapter the three great character types in the criminal class: the instinctive criminal, in whom the tendency toward a life of crime is inborn; the habitual criminal, who acquires the habit of crime from his surroundings; and the single offender, who, while committing a single offense, never becomes a criminal in the strictest sense. These three distinct classes of criminals, whom we might style the degenerates, the derelicts, and the accidental offenders, need to be recognized in our criminal law and to be dealt with differently by our criminal courts and correctional institutions. The instinctive criminal can scarcely be adjusted to normal social life. He is, as we have already seen, essentially a defective, usually more or less feeble-minded. Reformation in the fullest sense of the word is almost out of the question in his case. The proper policy for society with reference to the instinctive criminal class, which constitutes but a small portion of our total criminal population, would be segregation for life. Practically, of course, this may have its difficulties until we perfect our means of discovering slight mental defects in individuals which make them incapable of social adjustment, but practically, also, we have found means of recognizing this type by such marks as incorrigibility, recidivism, and the stigmata of degeneracy. The habitual criminal, who originally was a normal person, can be, at least in the early part of his career, fully reformed. Children and adolescents, even though habitual offenders, are easily susceptible of reformation, but this is difficult with the adult habitual offender past thirty years of age who has a long criminal record behind him. Like the instinctive criminal, he is scarcely capable of reformation. Hardened habitual offenders, and especially professional criminals, should, therefore, be sentenced upon indeterminate sentences, terminable only when adequate evidence of their reformation has been secured. This can best be accomplished by what is known as the "habitual criminal act," providing that persons guilty of three or four felonies shall be sent to prison for life, to be released only upon satisfactory evidence of reformation.