1. 1. Dick toxin contains a mixture of antigens for which specific antibodies exist in the sera of horses immunized for the production of scarlatinal antitoxin.2. 2. At least eight distinct precipitin systems are represented in a mixture of commercial antitoxin and standard erythrogenic toxin employed in this laboratory.3. Several methods of identifying individual precipitin systems, based on the Oudin technic, have been examined: 1. a. Specific adsorption of one antibody from the serum gives the most unequivocal results. 2. b. Replacement of the antigen layer on agar in which zones have been established is a reliable method, but produces some unexplained effects. 3. c. Agreement between the slopes of lines representing the relation between concentration of antigen and rate of migration should be used only as supportive evidence when dealing with ill-defined preparations. 4. 4. At least one antigen present in Dick toxin, antigen A, is derived from the heart-infusion broth used in toxin production.5. 5. The erythrogenic toxin proper is represented by the fourth zone (D) in tubes containing our standard toxin and antitoxin.
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