1. In rabbits, guinea pigs, and mice pneumococcus autolysate antitoxin has no effect against generalized infection by the pneumococcus.
2. In a large proportion of cases of pneumonia and sepsis caused by the intratracheal inoculation of large amounts of living pneumococci in normal or sensitized guinea pigs, autolysate antitoxin saves the animal.
3. The autolysate antitoxin is protective in most cases of pneumonia and sepsis caused by the intratracheal inoculation of small amounts of living pneumococci combined with sublethal doses of staphylococcus toxin.
4. These experiments indicate that in pneumococcus pneumonia of guinea pigs the autolysate toxin or toxins are elaborated only in the lungs.