Anybody who has been engaged in training hypnotized subjects knows that these insignificant signs constitute one of the chief sources of error. Some of the leading modern investigators in the domain of hypnotism - Charcot and Heidenhain, for instance - were misled by them at the time they thought they had discovered new physical reflexes in hypnosis. But in 1904, by which time suggestion had been sufficiently investigated to prevent such an occurrence, a psychologist should not have fallen into an error that had been made more than twenty years previously. It is necessary to make these remarks openly, no matter how highly we may prize Stumpf's services to psychology in other respects. As may be seen from the above report, Stumpf made the mistake of believing that he must see the signs if any were given. Since this was not the case, he simply excluded the presence either of voluntary signs - te., tricks - or of involuntary ones. But a psychologist like Stumpf could not help knowing that it is especially the involuntary signs that may be so delicate that not only the person who makes them is unaware that he is so doing, but even the spectators also are unable to detect them unless they employ special instruments for the purpose.

But the main point is this: signs that are imperceptible to others are nevertheless perceived by a subject trained to do so, no matter whether that subject be a human being or an animal. Stumpfs mistaken report has led to the propagation of the erroneous notion that a horse can be taught to extract square-roots, to perform the most complicated calculations, and be generally educated by a method of instruction like that employed in primary schools. The chief point for the experimenter is not, as Stumpf thought, that he ought to be able to perceive signs, but that he should work under conditions that render it impossible for signs to be made. Stumpf ought from the very first to have made use of that critical system of research that alone has been employed for the last twenty years by persons making experiments in connection with telepathy, clairvoyance, and the action of drugs at a distance - a domain I shall treat of in the last chapter. Since he had failed to draw from the experiences of the investigators of hypnotism and suggestion those conclusions requisite for the purposes of his investigations, he was bound to come to grief over Clever Hans.1

I have intentionally gone into the case of Clever Hans in detail, because it shows in the clearest manner possible what hypnotism has taught those who are conversant with that subject It is certain that the investigation of many other experimental researches made by some psychologists would bring to light the existence of the same source of error that I have demonstrated in the case of Clever Hans. Only, in the latter case, the error produced such serious consequences; for the horse that was supposed to be able to calculate not only created an immense sensation, but even led a well-known professional psychologist to pen one of the most absurd expert reports ever drawn up.

Hypnotism has, moreover, helped us to understand many erroneous scientific theories by the light it has thrown on the effects of auto-suggestion on investigators. Soury has published a study of a case of scientific auto-suggestion affecting several Italian physicians. Rainaldi and Giacomo Lombroso had believed that it was possible to excite certain brain centres and contract the related muscles, by mechanically irritating the scalp above those centres. Soury shows convincingly how doubtful the doctrine of localization is, and that every author always succeeds in causing contractions in accordance with his own views as to motor centres. Similar errors were very prevalent in the early days of hypnotic research. But we find a very similar auto-suggestive process outside the domain of hypnotism, as, for instance, when authors discover exactly what they want. Auto-suggestion is a hindrance to objective contemplation.

1 Later on, after I had given him the correct explanation privately and publicly, Stumpf relinquished his erroneous views when he was a member of a second committee. Unfortunately, he did not make a public admission of his error, as he was in duty bound to do; on the contrary, he fogged the issue by representing, that in his first report he only denied that voluntary signs had been made. That he was also on the look-out for involuntary signs, and did most emphatically deny that any such were made, is irrefutably proved by the report reproduced above, in which I have italicized the sentences relating to this point. In making the statement that he only dealt with the question of tricks - i.e., intentional signs - in his first report, Stumpf has said that which is substantially untrue.

It was also the influence of modern researches in hypnosis and suggestion that first shed a brighter light on that domain which we call the psychology of crowds. Among the investigators who have worked in this domain I may mention Tarde, Sighele, Sidis, Lombroso, Friedmann, Bechterew, Binet, Loewenfeld, Le Bon, Bleuler, Straticb. The soul of a crowd is not merely a combination of the souls of the individuals composing it; on the contrary, it presents certain peculiarities. So, too, the suggestibility of a crowd is of a different nature to that of the individual. Even if opinions differ as to how it happens that a crowd is often influenced by factors that have no effect on the individual, still all agree that the suggestibility of a crowd is something special. Loewenfeld thinks it is elective in that it is not absolutely greater than that of the individual, but, at the most, heightened in a definite direction. Moral contagion, which had already been discussed long before hypnotism, is closely connected with suggestion; and, as Tarde has rightly pointed out, suggestibility is the condition necessary for it to prove effective.

Sighele expresses similar views: - "It is quite clear to me that this suggestion is the cause of the movements and actions of crowds, and that a cry raised by some individual in the midst of a crowd, or the word of a speaker, or the act of some desperado, so seizes the whole mass in its suggestive grasp, that it is carried away to acts of destruction like a wild and will-less herd." Certainly the catchword "suggestion" alone does not explain the psychology of crowds. Numerous other psychological factors play a part, and these have been pointed out in a more or less convincing manner by the authors mentioned above. But whether we are dealing with social or political events, or with artistic tendencies and scientific currents of thought, the suggestibility of the crowd invariably makes itself felt in a particular direction. The same thing occurs where questions of religion or civilization are concerned, even should, in the latter case, the question be merely one of fashion in dress. The part that is also played in religious questions by the suggestibility of crowds is evident from the enormous influence exerted on huge multitudes by the religious hallucinations of any hysterical female who imagines she has seen the Madonna. We find the same thing occurring with those founders of sects, who have known how to infect thousands and thousands of people with their own peculiar hallucinations.