Suggestion, or rather Autosuggestion, is quite a new subject, and yet at the same time it is as old as the world. It is new in the sense that until now it has been wrongly studied and in consequence wrongly understood; it is old because it dates from the appearance of man on the Earth. In fact, autosuggestion is an instrument that we possess at birth and in this instrument, or rather in this force, resides a marvellous and incalculable power, which according to circumstances produces the best or the worst results. Knowledge of this force is useful to each one of us, but it is peculiarly indispensable to doctors, magistrates, lawyers, and to those engaged in the work of education. By knowing how to practice it consciously it is possible in the first place to avoid provoking in others bad auto-suggestions which may have disastrous consequences, and secondly, consciously to provoke good ones instead, thus bringing physical health to the sick, and moral health to the neurotic and the erring, the unconscious victims of anterior autosuggestions, and to guide into the right path those who had a tendency to take the wrong one.