During the past year we have frequently used antiserums experimentally in cases of acute insanity because we have been led to believe from our observations that many of these cases, either primarily or secondarily, are suffering from bacterial infection. The grounds upon which we base this belief are that we frequently find hyperleucocytosis, and in forty-eight out of seventy-six cases examined we have found bacterial agglutinines in the blood which do not exist in the blood of healthy people.