A post-hypnotic suggestion will be more readily fulfilled when the moment for its execution is determined by an external sign; but successful cases in which no such sign has been employed are anything but rare. There is often a certain amount of unpunctuality in the fulfilment of a suggestion when no concrete external sign is used; for example, the suggestion will be carried out in three-quarters of an hour instead of an hour. Occasionally punctuality is very marked. Delbceuf made post-hypnotic suggestions to various persons by telling them to perform a certain act after so many minutes - say, a thousand minutes. In many cases, even with persons who were otherwise not able to estimate time rightly, striking punctuality was shown. Bramwell has made numerous experiments for the purpose of fixing the time in this respect. For example, he told a young lady aged nineteen to make the sign of the cross after the lapse of 4,335 minutes. In spite of the fact that she had forgotten all about the suggestion she fulfilled it accurately. Further experiments of this nature gave strikingly accurate results, no error exceeded five minutes, and Bramwell ascribed all to hesitation on the part of the subject.

The subject was requested, in hypnosis, to transpose the hours and minutes, and did make miscalculations; but she nevertheless carried out the primary suggestion correctly, sometimes even when asleep at night. At Hansen's instigation Sommer made a few experiments of the same kind, but on a smaller scale. A student was told that he was to fall asleep when ordered; then, two minutes later, he was to talk about skating; after this he was to sit still for a minute, and finally jump up and shout "Hurrah! for Giessen." The suggestion was fulfilled to the second. The subject stated subsequently that he only remembered counting up to thirty-one or thirty-two, although he wanted to count up to one hundred and twenty to complete the two minutes. Sommer considers that counting would enable the subject to keep to the time-limit, but that loss of memory intervenes.

I will point out a frequent source of error in experiments of this nature: this is the behaviour of the spectators. They look at the clock at the appointed time, or make some other unconscious signal that the right moment has arrived. I call particular attention to this so that the time may be accurately observed.

The older mesmerists, Nasse and Eschenmayer for example, made investigations about this faculty of somnambulic subjects for exactly reckoning time. But it is an exaggeration to maintain that as a rule the time is reckoned accurately. The punctuality displayed by hypnotics is very like that of people who can voluntarily awake from their usual sleep at any hour they please. According to statistics collected by Childe many people are capable of doing this. The ancient Hindoos studied this subjective faculty for reckoning time very industriously. It is sometimes called the mental clock ("Kopfuhr," Du Prel).

A third way of fixing the time at which a post-hypnotic suggestion is to be fulfilled has been thoroughly investigated by Gurney and Pierre Janet. For example, I say to a subject, X., "When I shuffle my feet for the tenth time after you wake up, you will burst out laughing." X. wakes up quite oblivious of my order,, and I engage him in conversation and shuffle with my feet several times without his taking any notice; at the tenth shuffle he gives a loud laugh. I repeated the experiment on another occasion, and when I had shuffled my feet four times I asked X. if he heard the shuffling; he replied "No." I went on quietly talking, and at the same time gave six more shuffles with my feet, upon which the suggestion was carried out. In most cases, however, the result was not quite so accurate - the post-hypnotic suggestion was certainly fulfilled, but not at the right signal.

Many deferred suggestions resemble those suggestions in which the moment of fulfilment is determined by counting (Gurney). Post-hypnotic deferred suggestions can be made in two ways; for example, on the 3rd of May I say to a person who calls on me every day, "On the 6th of June, when you come into my room, you will see me with a black face, and you will laugh at me." The suggestion succeeds. But here a fixed date is named which helps the subject to carry out the suggestion in the same way as the striking of the clock in the case first quoted. Delbceuf, in particular, has pointed out the importance of this. It would have been another matter if I had made the suggestion thus: "On the thirty-fifth day, reckoning from to-day, you will come into my room and see me with a black face, etc." According to Gurney's observations, suggestions of this kind succeed, and my own experiments confirm him. An example may make this sort of suggestion clearer. I suggested once to X., "You will come to my house on the sixteenth Tuesday, reckoning from last Tuesday, and will abuse all the people present," etc This suggestion succeeded completely, although no fixed date was named.

I have as yet only discussed the manner of determining the point of time for the carrying out of the post-hypnotic suggestion. I now come to the question, What is the condition of the subject while carrying out the post-hypnotic suggestion? Dumontpallier, Beaunis, and Liegeois observed that posthypnotic suggestions were certainly not carried out in the waking state, even if the action took place after the awakening from hypnosis. The question has led to a lively discussion; and Forel and Gurney have shown that the post-hypnotic suggestion may be carried out in very different states. A few examples will make this clear to the reader.

A man (X.), thirty years old, is in the hypnotic state. I say to him, "When you wake, directly I cross my knees you will take the inkstand from the table and put it on the chair." He wakes at my order, and I talk to him. After a time I cross my knees; he begins to stare at the inkstand and hardly answers me. He goes to the table, takes the inkstand and puts it on the chair; upon which I suggest to him that he sees his brother, that he is eating his dinner, etc., all of which suggestions he accepts. I am obliged to re-awaken him to put an end to this new state of suggestibility. After waking he remembers absolutely nothing.