Crystalline cholera toxin and toxoid.

The exo-enterotoxin of Vibrio cholerae has been obtained in crystalline form. A solution of the crystalline protein was equal in potency to the parent pure toxin in both choleragenicity and skin reactivity. Crystals of the natural toxoid, choleragenoid, resemble those of the toxin in appearance. A solution of crystalline choleragenoid was equivalent to the parent preparation in the flocculation test.