We have referred elsewhere to the therapeutic accomplishments of the saints during the middle ages. We will here only dwell upon the influence which the devil, the Christian successor of the ancient evil spirit, has exerted upon the medical views of all classes of the people. This influence was very great. The devil and his subordinate infernal spirits were considered the “disturbers of peace” in the health of humanity. Disease in its various forms was their work; they resolved to inflict it either from inherent villainy or as incited by various magical arts of evil men. It was especially the latter form of diabolical activity that, during the entire middle ages and during a considerable part of modern times, was accepted as uncontestedly authentic, and the imagination of mankind at that period was inexhaustible in inventing the greatest variety of infamous actions which the devil was able to perform either of his own accord or as summoned by incantations. Any one desiring to acquaint himself thoroughly with these delusive ideas should read the work of the Friar Cæsarius, who lived about 1225, in the Rhenish-Cistercian monastery of Heisterbach. Naturally, we are only interested in the medical acts which the devil was always ready to perform. According to the history of medical superstition, the devil, who was invoked by various spells or appeared of his own volition, was able to influence each individual bodily organ in a manner most disagreeable to the possessor of the same. Neither were the Prince of Hell and his hosts always satisfied to tease and to plague an individual being, but very frequently they carried on this business wholesale. They threw themselves upon the entire population of a country, and caused sickness in all who crossed their path. The great epidemic of St. Vitus’s dance of the fourteenth century, for instance, was considered to be the work of the devil, and the clergy busied themselves in driving out this devil’s pest by means of sprinkling holy water and by the utterance of conjuring formulas.