1. In passively sensitized animals bacterial anaphylaxis has been produced, in vivo and in vitro, with haptens from B. lactis aerogenes, the pneumobacillus, and a yeast.
2. The smallest amount of hapten causing fatal anaphylaxis is less than the minimal amount of protein which will cause death in properly sensitized animals.
3. The haptens used were largely carbohydrates, and gave none of the protein reactions, but since they did contain a small amount of nitrogen we cannot yet assert positively that carbohydrate alone will produce shock.
4. Since haptens will not sensitize animals we must conclude that the anaphylactogenic and shock-producing parts of the antigen are not identical.
5. These experiments provide further evidence of the close relationship of precipitins to anaphylaxis.