"A phenomenon of which it is easy to establish the presence but which it is not easy to explain. It must be classed among those phenomena of a hypnotic order. In a group every sentiment and act is contagious, and contagious to such a degree that an individual readily sacrifices his personal interest to the collective interest. This is an aptitude very contrary to his nature, and of which man is scarcely capable except when he makes part of a group."
