Masturbation is possible only under the two following conditions: first there must be an opportunity to indulge in secret; next there must be a possibility of indulging. Hence by frustrating these conditions we can prevent onanism, the wishes of the onanist to the contrary notwithstanding. The opportunities for onanism are all embraced under one term, _isolation_. It is necessary for the onanist to be alone. Hence watchfulness, that precaution which makes the young man constantly observes, which exposes him every moment to detection and consequently to shame, to reproaches and to punishment for his fault, is a powerful means of preventing it. Watchfulness should be particularly practised over young people, when they are undressed, in bed, in the bath or in the privy. Hence the young patient should undress, go to bed and rise under your inspection. If this be not sufficient, he should share your bed. This measure is frequently the only way to prevent onanism. In large boarding schools there should be no private rooms: the sleeping chambers should be extensive, and a lamp, which would give sufficient light to assist your watchfulness, but not enough to prevent sleep, should burn in it all night. The masters and those who have charge of the pupils ought to examine in silence at different hours and the most perfect quiet should exist in the apartment. Here too the hours of retirement and of rising should be calculated according to the ages, so that the suspected or guilty might never go to bed except to sleep. Be watchful of those who stay long in privies: those however with ample accommodations are not so dangerous as those which are single. In some schools the doors of the privies are open at the top, so that an adult can look into them. Need we add that persons who are suspected should be watched in the bath. Onanism is executed with the hand and thighs on the sexual parts or by rubbing these parts against external bodies. Different modes have been proposed to obviate and prevent these. The most simple of all is to oblige the children to keep their hands out of bed. This plan when it can be observed is often sufficient, particularly in boys. Besides this we knew of only one remedy, the purpose of what can be concealed, viz., the application of a cold cataplasm to the sexual parts, a plan we have recommended several times. Pavet de Courtielle proposes the use of a chemise reaching below the feet and which is drawn together at the bottom: this remedy may be efficacious. The remedies which remain to be treated of are essentially coercive: hence the chance of success is smaller the older and stronger the patients are.