l. The total antitoxin binding value of a toxoid of Cl. welchii, Type B (the "lamb dysentery bacillus") has a direct bearing on its immunizing capacity. The more antitoxin a toxoid binds, the greater is the degree of immunity produced by it.
2. Atoxic toxoid, rendered slightly toxic by the addition of the toxins of Cl. welchii, Types A or B proved superior as an antigen to the toxoid itself. The addition of the toxin of Cl. septique did not increase the immunizing value of toxoids.
3. The intravenous injection of 4-6 sub-lethal doses of Type B toxin, within 4-5 hours may so immunize a guinea-pig that it resists a fatal dose of toxin 24 hours later.
4. Alum-precipitated toxoids proved, on the whole, inferior as antigens to the toxoids, themselves. The addition of agar, colloidal iron and saponin to toxoids did not increase their immunizing power.
5. The washed zinc chloride precipitates of toxoids proved superior as antigens to the toxoids themselves. The solubility of the precipitate appears to have a direct bearing on the degree of immunity produced.
6. Washed living or washed boiled suspensions of Type B bacilli (free from demonstrable toxin) stimulated the formation of antitoxin when injected into goats and guinea-pigs.
7. Washed suspensions of Type B bacilli, heated at 60⁰ C, for half-an-hour, contain a toxic material, not neutralizable by anti-toxin.