Antitoxin Titers Following Immunization with Protamine-Precipitated Diphtheria Toxoid *

ONE of us has recently described the preparation and immunizing properties of protamine-precipitated diphtheria toxoid.1 This new form of diphtheria toxoid (which contains less than 0.1 per cent alum) was found to produce less reaction than either "fluid" or alum-precipitated toxoid when tested by intradermal injection in human adults. Its nitrogen content, including that of the protamine present, is 0.006 t mg. per Lf. (Limes flocculation dose), considerably less than that of alum-precipitated toxoid. It is almost entirely free of bacillary protein. Guinea pigs produced 2 to 3 units of antitoxin 4 weeks after a subcutaneous injection of one dose (20 to 25 Lf.) and approximately 7 units 6 weeks after a second dose. The antigenicity of the new product was also measured by means of the Schick test in children and adults. Ninety-six per cent of 554 Schick-positive children who received one dose (20 to 25 Lf.) became Schick-negative. The interval between the injection and