Residue antigen recognizable by the precipitin test can be prepared from yeast as from bacteria.

The active material appears to be identical with a complex carbohydrate, the "yeast gum" of Salkowski.

In the purest form of it obtained small amounts of both nitrogen and phosphorus are still present, either as impurities or as part of the molecule.

The yeast gum is not antigenic in the sense of producing antibodies.

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