Filtrates of fluid cultures of Bact. enteritidis usually are toxic for rabbits and mice, but not guinea-pigs, when injected intravenously, but are apparently harmless when given by other routes. The time between the introduction of the poisonous fluids into the blood stream and symptoms of intoxication seems to bear no relation to the size of the dose, but is constantly about 40 to 45 minutes, whether the amount given be lethal or sublethal. The symptoms are restlessness, dyspnea, prostration, often diarrhea, and either death within 1 to 12 hours or slow recovery. The acute stage lasts about from 30 minutes to 1 hour. The most conspicuous finding at necropsy is marked general vasodilation, with edema of the lungs, and in many animals, both agglutination and platelet thrombi in the capillaries. The occurrence of toxicity in cultures is variable, but it may be found in any medium in which the organism grows. The poisons are thermostabile. Toxicity of broth and synthetic medium cultures appears after the number of living cells has reached its maximum and has begun to decrease. The toxic properties are demonstrable not only in filtrates of fluid cultures, but in autolysates, and with dead and living bacteria. Toxic materials, in dilutions in which no protein could be detected, stimulate the production of antibodies. The serum of rabbits immunized with them bestows definite protection on other rabbits when injected intravenously. Similar poisons are demonstrable with other members of the colon-typhoid group. The results appear to indicate that the poison demonstrated by these experiments is within the bacterial cells, is set free on cell disintegration, and probably is not a true soluble toxin.