Since the publication by Ewald and Hoegyes of their epoch making experiments on the semi circular canals oi animals and the discovery of the underlying laws of labyrinthine physiology, extensive researches have been conducted at the clinics of Vienna and Berlin on the human laby rinth. While the latter have been but supple mental to the classical work of the above named pioneers, they have served to reduce the subject to a practical basis and to evolve a new and valu able method of diagnosis of conditions hitherto obscure. Nystagmus, which has until recent years, been associated almost entirely with con genital or early acquired optical defects, or in an indefinite way, with lesions of the inner ear, has become one of the most important aids in differ ential diagnosis and greatly amplified the scope and efficiency of the aurist.