To understand this phenomenon it is necessary to bear in mind certain recent physiological discoveries. We know to-day that by various processes an individual may be brought into such a condition that, having entirely lost his conscious personality, he obeys all the suggestions of the operator who has deprived him of it, and commits acts in utter contradiction with his character and habits. The most careful observations seem to prove that an individual immerged for some length of time in a crowd in action soon finds himself--either in consequence of the magnetic influence given out by the crowd, or from some other cause of which we are ignorant--in a special state, which much resembles the state of fascination in which the hypnotised individual finds himself in the hands of the hypnotiser. The activity of the brain being paralysed in the case of the hypnotised subject, the latter becomes the slave of all the unconscious activities of his spinal cord, which the hypnotiser directs at will. The conscious personality has entirely vanished; will and discernment are lost. All feelings and thoughts are bent in the direction determined by the hypnotiser. Such also is approximately the state of the individual forming part of a psychological crowd. He is no longer conscious of his acts. In his case, as in the case of the hypnotised subject, at the same time that certain faculties are destroyed, others may be brought to a high degree of exaltation. Under the influence of a suggestion, he will undertake the accomplishment of certain acts with irresistible impetuosity. This impetuosity is the more irresistible in the case of crowds than in that of the hypnotised subject, from the fact that, the suggestion being the same for all the individuals of the crowd, it gains in strength by reciprocity. The individualities in the crowd who might possess a personality sufficiently strong to resist the suggestion are too few in number to struggle against the current. At the utmost, they may be able to attempt a diversion by means of different suggestions. It is in this way, for instance, that a happy expression, an image opportunely evoked, have occasionally deterred crowds from the most bloodthirsty acts. We see, then, that the disappearance of the conscious personality, the predominance of the unconscious personality, the turning by means of suggestion and contagion of feelings and ideas in an identical direction, the tendency to immediately transform the suggested ideas into acts; these, we see, are the principal characteristics of the individual forming part of a crowd. He is no longer himself, but has become an automaton who has ceased to be guided by his will.