We might cite here numerous pathological conditions of mind that very plainly spring from physical causes and to which the instructor has to give attention just as much as the physician. Instead, however, of citing particular cases, we will refer to three little treatises that are in the highest degree instructive on this point, not only for teachers exclusively but also for all who have to do with children. Dr. MAXIMILIAN BRESGEN, specialist in diseases of the nose and throat at Frankfort on the Main, has published at the house of Leopold Voss in Hamburg (1890) a brochure entitled _Ueber die Bedeutung behinderter Nasenathmung nebst besonderer Berücksichtigung der daraus hervorgehenden Gedächtniss- und Geistesschwäche_. A treatise of like character is that of Dr. med. LENZMANN of Duisburg, entitled _Ueber den schädlichen Einfluss der behinderten Nasenathmung auf die körperliche und geistige Entwickelung des Kindes_, Bielefeld, 1890, Anders Verlag. Both treatises contain, among other things not to be considered here, instructive examples of the rise and disappearance of that morbid mental condition to which Hack first directed notice in Germany but which elsewhere became known through the researches of the Dutch physician Guye by the name of _Aprosesia nasalis_. The third treatise is by Dr. med. RALF WIECHMANN, specialist for nervous diseases at Brunswick, and bears the title _Eine sogenannte Veitstanzepidemie in Wildbad_, Leipsic, 1890, Verlag von Georg Thieme. By St. Vitus’s dance (Ger. _Veitstanz_) we understand the disease of which the well-known symptoms are involuntary muscular twitchings usually accompanied by severe or light psychical disturbances, known in medicine by the name of _chorea minor_ and _chorea rhythmica_, and sometimes occurring in epidemics. At the school in Wildbad the number of the afflicted children rose in the course of time to twenty-six. Wiechmann expatiates at length in his book on the character of the contagion, and arrives through an exhaustive use of the existing literature on the subject at the result, that there was present in the individual children attacked substantially a physical predisposition, an unstable nervous system. As the first children attacked were not removed, the convulsive motions were seen and perceptually taken up by the other children, who were just approaching the period of puberty and labored under hereditary predispositions. “Once these images had entered perceptually into the unstable brain, they became competent to operate as stimuli and to be translated into involuntary muscular motions.”