Following up my observations made upon the blood of patients suffering from acute continuous mania read before this Association at the autumn meeting, I have been able to observe three cases of acute continuous mania in adults which relapsed while in the asylum. The results of the first series of observations were that in every case of acute continuous mania there existed a leucocytosis which persisted after recovery indefinitely. I advanced the theory that this leucocytosis was a protective leucocytosis. In the three patients who relapsed the leucocytosis was found to have fallen to below 13,000 per c.mm. of blood, instead of being nearer 20,000 per c.mm. of blood, which is characteristic of the recovered cases of mania. The polymorphonuclear leucocytes averaged 60 per cent, in two of these patients, and 47 per cent, in the third. In one of these patients the attack passed off in two days, and the leucocytosis at once rose to 25,000 per c.mm. of blood. The other two patients passed into a definite second attack, and their leucocytes averaged 15,000 to 16,000 per c.mm. of blood, with a polymorphonuclear percentage of 60 or below 60. The fact that the leucocytosis fell in each patient at the commencement of the attack, and rose at once in the patient who recovered from the relapse, strengthens the hypothesis that acute continuous mania is an infective disorder, and that immunity from maniacal attacks rests upon the resistive power of the individual patient. This hypothesis receives further support from the fact that there exists in the blood of patients suffering from acute mania a specific agglutinin. During the month of November a patient suffering from acute mania was admitted to Murthly. The patient was so ill that I did not think she would live many days. I isolated from the blood a very small coccus, which was a pure growth, but, as the patient was exhausted, I regarded the organism as a terminal infection. The patient improved, however, and three weeks later I tested the agglutinative power of her serum upon this organism in a dilution of 1 in 30. Agglutination was complete in three hours, while the serum of a member of the staff in a dilution of 1 in 20 produced no action in twenty hours. Since then I have made fifty agglutination tests with this organism. Only ten of these cases, however, have been pure cases of continuous mania. Eight gave a decided definite agglutination, one was doubtful, and the tenth—one of the patients above noted, who relapsed—gave no reaction. No “control” serum ever gave a reaction, nor did the serum of these patients suffering from mania agglutinate other organisms. The agglutinin in the blood was therefore a specific agglutinin.