Clxxxiii. Purification of Diphtheria Toxoid. by Peter Joseph Moloney and Morton

METHODS' for the purification of diphtheria toxoid may be divided into two classes; those which give a moderate degree of purification and a high yield, and those which give a high degree of purification and a yield which varies within wide limits. Among the latter is the method first applied to toxin by Glenny and Walpole [1915] and later modified by Watson and Wallace [1924] for toxin and by Watson and Langstaff [1926] for toxoid. The method of Watson and Langstaff depends on the fact that toxoid is precipitated from aqueous solution in the PH range 3-8 to 4-4. The precipitated toxoid is in a high state of purity relative to crude toxoid solution but yields may vary with different toxoid preparations from 5 to 90 %. It seemed reasonable to assume that the low yields which are often obtained by this method might be due not to true solubility of toxoid in the acid solution but either to a slow rate of precipitation or to the presence of substances in the solution which interfere with precipitation. Granting the correctness of either of these suppositions, a toxoid once precipitated should not redissolve in a solution of pl1 3-8 to 4.4. The work which was involved in attempts to prove or disprove this assumption regarding the solubility of toxoid within a certain range of acidity resulted in the methods of purification which are described in this paper. In brief, these methods depend upon precipitation of toxoid in the PH range 3-8 to 4-4 by precipitating agents which may also precipitate much other material, followed by removal, under the same conditions of acidity, of the precipitating agent and consequently of other material soluble within the range of insolubility of the toxoid. METHOD I.