One of the most interesting phases of hypnotism is that of post-hypnotic suggestion, to which reference has already been made. It is true that a suggestion made during the hypnotic condition as to what a person will do after coming out of the hypnotic sleep may be carried out. A certain professional hypnotizer claims that once he has hypnotized a person he can keep that person forever after under his influence by means of post-hypnotic suggestion. He says to him while in the hypnotic sleep: “Whenever I look at you, or point at you, you will fall asleep. No one can hypnotize you but me. Whenever I try to hypnotize you, you will fall asleep.” He says further: “Suggest to a subject while he is sound asleep that in eight weeks he will mail you a letter with a blank piece of note paper inside, and during the intervening period you may yourself forget the occurrence, but in exactly eight weeks he will carry out the suggestion. Suggestions of this nature are always carried out, especially when the suggestion is to take effect on some certain day or date named. Suggest to a subject that in ninety days from a given date he will come to your house with his coat on inside out, and he will most certainly do so.” The same writer also definitely claims that he can hypnotize people against their wills. If this were true, what a terrible power would a shrewd, evil-minded criminal have to compel the execution of any of his plans! We hope to show that it is not true; but we must admit that many scientific men have tried experiments which they believe demonstrate beyond a doubt that criminal use can be and is made of hypnotic influence. If it were possible to make a person follow out any line of conduct while actually under hypnotic influence it would be bad enough; but the use of posthypnotic suggestion opens a yet more far-reaching and dangerous avenue.