Mental diseases, and especially hysteria, have, from the earliest times to the present, exercised a tremendous influence upon the current metaphysical conception of the universe and upon the whole mental development, and that precisely because they not only occurred sporadically, but, as we shall soon see, attacked the masses In the form of epidemics and so became of the higheet significance and importance for the life of society as a whole, says Popular Science Monthly. Religious enthusiasm and proneness to the mystic and the occult formed, even in the highest antiquity, an important factor of those degenerate and hysterical Individuals who entertained the delusion that they were in communication with good or bad spirits, and who by that channel influenced the masses not a little. A great number of the priestesses who delivered oracular responses to the Greeks "with strong quaking of their bodies" were psychopathic subjects undergoing the hysterical convulsione well known to us to-day. Henee epilepsy, whlch in those days was not discriminated from hysterical cramps, came to be called the morbus sacer, or sacred disease. Plutarch, in his description of the Pythian priestese, delineates the typical Image of a hysterical subject who, in ecstatic convulsión, stammered unintelligible words, into which the priests injected some sense. But hysteria, with its inclination to religious enthusiasm, was not limited to separate persons. On the contrary, we meet with it among all peoples and in all periods of history, and among all peoples we meet with it in the form of epidemie of various kinds. But never did this disease find a better or more fertile soil in which to thrive than in the middle ages of northern Europe, marked as they werL by ignorance and superstition, and, accordingly, we find that epidemics of hysteria then assumed dimensions surpassing those of any similar outbursts in other centuries. A great many fine books have been written about the individual and epidemie crazes of those ages. The French huve made particularly careful researches into the matter. Calmeil describes a great number of hysterical epidemics of different forms. One of the principal eruptions in Germany was demonomania or ttufulswahn. "In the year 1549," says Calmeil, "a delusion called vaudoisie prevailed in Artois, that the devils carried many secretly in the night to the assemblies, where compacts were made with Satan. Without knowing how, the participants of the nocturnal meetings found themselves next morning back in their dwellings."