1. The union of fresh serum of pregnant or immunized animals with the corresponding boiled protein (substratum) is accompanied by the formation of poisonous substances.
2. The poison originates from the serum as a result of its autodigestion, and not from the substratum.
3. The process of autodigestion may be determined by the specific or non-specific removal of the antitrypsin of the serum.
4. The poisons originating from the serum are toxic only for homologous animals.
5. The autodigestion of the serum, if allowed to proceed far enough, may go beyond the toxic stage.
6. The biological properties of these poisons indicate their close similarity to the anaphylatoxin, and suggest that the anaphylatoxin of Friedberger is a product of the autodigestion of serum, and not of the protein outside of the serum.