1. When living or dead tubercle bacilli and their products are placed in direct contact with the leptomeninges of hypersensitive (tuberculous) animals, there is a definite clinical and pathological response.
2. The clinical response is characterized by an onset of weakness, twitchings, convulsions and death of the animal within 6 to 12 hours.
3. Histologically the central nervous system shows an extensive polymorphonuclear exudate distributed throughout the subarachnoid spaces of the brain and extending into the perivascular spaces.
4. The intensity of the response is directly proportional to the quantity of visceral tuberculosis or to the dose of tuberculin employed.
5. When small quantities of tuberculin are employed so as to permit the animal to survive longer than 24 hours, there is an exudate found in the sulci and at the base of the brain which is characterized by small lymphocytes.
6. The non-tuberculous animals when inoculated with tuberculin or tubercle bacilli revealed no clinical or pathological response. The tuberculous animals, on the other hand, when inoculated with glycerine broth always responded by a definite but slight polymorphonuclear exudate.
7. The possible relationship of the allergic state to postinfectious complications of the central nervous system is discussed.