1. Tubercle bacilli injected into the peritoneal cavities of tuberculous guinea pigs, rats, rabbits, dogs, and monkeys, rapidly disappear from the peritoneal fluids, while persisting in the peritoneal fluids of normal control animals.
2. This disappearance is in part due to an adhesion of the injected bacilli to the peritoneal leucocytes and a fixation of the leucocytes on the omentum.
3. The injected tubercle bacilli can be recovered quantitatively from the peritoneal cavities of normal guinea pigs from one and one half to two hours after the injection, while from tuberculous guinea pigs only 65 per cent. of the bacilli can be recovered at this time.
4. Isolated peritoneal tissues from tuberculous guinea pigs have the power of destroying tubercle bacilli in vitro.
5. A second factor reducing the number of tubercle bacilli free in the peritoneal fluid is therefore an actual lysis of the bacilli.
6. The intraperitoneal lysis is not due solely to substances present in the circulating fluids, since the phenomenon cannot be produced by these fluids in vitro, and since a lytic power cannot be passively conferred even by a direct transfusion of blood from tuberculous to normal animals.
7. The intraperitoneal lysis is apparently due to specific changes in the fixed peritoneal cells of the tuberculous animals.