A blow, an illness, a fright, the stress of a prolonged emotion--any one of several causes may bring about this weird condition, of which I could give illustrative cases to a number that would fill many pages of this book.[47] Sometimes, though fortunately seldom, there may be--as in the case of BCA--a double or even a multiple dissociation, resulting in the development of two, three, four, or more secondary selves, which alternate with one another in a way productive of the most intense mental agony to the helpless victim. [47] A collection of such cases will be found in my book, "Scientific Mental Healing," pp. 124-155. But, after all, it is not necessary to insist on such extreme instances in order to demonstrate the essential instability and divisibility of that which we commonly have in mind when we speak of the "self." Dissociation of personality is in evidence every day in the pathetic symptomatology of the various insanities, and in the chronic, if often masked and unrecognized, memory lapses universal among sufferers from the manifold affections of hysteria, such as we dealt with in the chapter on "Dissociation and Disease." It is in evidence in the victims of alcoholic and drug excesses, who, in a very literal sense, may become "another person," and say and do things quite alien from their usual self, and concerning which their usual self afterward has no knowledge. Even normal sleep, albeit a wise provision for the rest and strengthening of the organism, involves dissociation. Still more strikingly is dissociation evident in the phenomena of the state of artificial sleep induced by hypnotism. It would carry us too far from the point now under consideration to enter here into any discussion of the nature and mechanism of hypnotism, that still widely misunderstood but marvelous agency, not simply for therapeutic purposes but for the study and exploration of man's inmost being. The thing of immediate importance is the fact that under the influence of hypnotism a person invariably develops a self more or less different from his ordinary waking, conscious self. Hypnotized, he is to all outward seeming oblivious to everything transpiring around him. But let the hypnotist speak to him, question him, and he instantly responds with answers so intelligent as to indicate that, in some respects, at all events, he is more alert and keen than when wide awake. Curiously enough, however, commands and suggestions given to him are, within certain limitations, accepted and acted upon, no matter how disagreeable or absurd they may be.