Prior to the discovery of the Wassermann reaction it was practically impossible to obtain a correct estimate of the incidence of syphilis amongst the insane, owing to the infrequency of physical signs in specific cases, and the difficulty of obtaining reliable histories. Experience has shown that in a large number of cases a positive Wassermann reaction with the serum may be the only evidence of syphilitic infection; more over, Dr. Mott (Archives of Neurology and Psychiatry, vol. vi) has shown that definite skin lesions are comparatively rare in general paralysis of the insane.