Although born criminals, habitual criminals, and recidivists should be carefully isolated from minor offenders, they nevertheless require institutes conducted on nearly similar principles. A prison, which is to punish, but at the same time to correct and redeem, demands strict discipline: in fact, milder punishments have very little effect and their constant repetition is harmful, although any exaggeration of brute force is more injurious than useful. Harshness may cow criminals, but does not improve them: on the contrary, it only serves to irritate them or to convert them into hypocrites. Even the adult offender should be looked upon in the light of a child or a moral invalid, who must be cured by a mixture of gentleness and severity, but gentleness should predominate, since criminals are naturally prone to vindictiveness and are apt to regard even slight punishments as unjust tortures. Even a too rigid adherence to the rule of silence may have a detrimental effect on the character of the prisoners. An old convict once said to Despine: "When you winked at slight offences against the rules, we used to talk more, but there was no harm in what we said. Now we talk less, but when we do, we blaspheme and plot evil." In Danish prisons under rigorous discipline, infractions of prison regulations amounted to 30%; more recently under milder rule such infractions only amount to 6%. In order to strengthen the sense of justice which, as we have said, is little developed in criminals, if indeed it is not altogether suffocated by ignoble passions, it is often advisable to appeal to their vanity and self-esteem to aid in maintaining discipline and increasing industry, by constituting them judges of each other's conduct. Obermayer used to divide the convicts into small groups and ask them to elect their own superintendents and teachers, thus establishing a spirit of good-comradeship and rendering possible a system of detailed and individual instruction, the sole kind that is really efficacious. The 385 convicts at Detroit showed the highest percentage of efficiency, because they were divided into 21 classes with 28 teachers, all of whom, with the exception of one, were prisoners. It was noticed that the worst convicts were the best teachers (Pears, _Prisons and Reform_, 1872), which proves that even the most perverse elements may often be utilised for the improvement of others. Equally good was Despine's method of letting a certain time elapse before inflicting punishment, so that it should not be attributed to mere anger on his part. As soon as the infraction was noted, the prisoner was left to reflect on his conduct, and an hour later the teacher and Director came to show him the penalty prescribed by the regulations. Sometimes it was found efficacious to administer a rebuke and punishment to the whole group to which the offender belonged. Obermayer considered this method to be advantageous.