Cases of mental disease which give definite mental symptoms and physical signs of the condition recognised and at present called general paralysis of the insane, and which, moreover give a Wassermann reaction, seem to be invariably due to syphilis, and to contain in many cases spirochætes in the cerebral substance. Out of seven such cases of well-marked general paralysis, which on death were examined for spirochætes by Dr. McIntosh, six cases showed the presence of spirochætes. The seventh case was regarded as doubtful.