In the phenomena of contagion words and symbols play a powerful part. They are both a rallying-point and an outlet for the emotions of a crowd. These words or symbols may be wholly incongruous with the real needs of a people, but provided they are sufficiently familiar they will serve their purpose. And the more primitive the type of mind represented by the mass of the people the more powerfully these symbols operate. Shakespeare's portrayal of the crowd in _Julius Cæsar_ remains eternally true. The skilled orator, playing on old feelings, using familiar terms, and invoking familiar ideas, finds a crowd quite plastic to his hands. It is for these reasons that there is so keen a struggle with political and social parties for a monopoly of good rallying cries, and a readiness to fix objectionable titles on their opponents. Patriotism, Little Englander, Jingo, The Church in Danger, Godless Education, etc. etc. Causes are materially helped or injured by these means. There is little or no consideration given to their justice or reasonableness; it is the image aroused that does the work. Psychological epidemics may in some cases be justly called normal in character. That is, they depend upon factors that are always in operation and which form a part of every social structure. A war fever or a commercial panic falls under this head. In other instances they depend upon abnormal conditions, upon the workings, perhaps, of some obscure nervous disease, and are of a pathological description. In yet other cases they represent a mixture of both. In such cases, for example, as that of the Medieval Flagellants or of the Dancing Mania, the presence of pathological elements is unmistakable. But neither of these epidemics could have occurred without a certain social preparation, and unless they had called into operation those principles of crowd psychology to which science has within recent years turned its attention, and which are normal factors in every society. These three classes of epidemics may be found in connection with subjects other than religious, but I am at present concerned with them only in that relation, and to point out that, in spite of their undesirable or admittedly pathologic character, they have yet served to keep supernaturalism alive and active.