N. Y. wIESE two preparations, toxin-antitoxin and toxoid, are now being widely used for immunization of infants and young children against diphtheria. Toxin-antitoxin has been longest in use. Behring was the first to employ it experimentally as an immunizing injection in man. His preparation was the undiluted toxic broth with its toxin nearly neutralized by antitoxin. He never gave a clear explanation of how he prepared and standardized it. The breaking out of the war delayed the practical utilization of toxin-antitoxin in Europe.Park and Zingher were the first to realize that by using the Schick test to determine the susceptibility of the children, and a retest to note the changes in reaction, we could study the immunizing effect of toxinantitoxin injections in human beings. We demonstrated that immunity developed in about 85 per cent of those receiving 3 injections of our 3 L + preparation at intervals of 1 week, and by 1917 we realized that it lasted in the great majority of cases for at least several years. We also tried giving it at intervals of 2 weeks, but the results were only moderately better. Schroder followed the Schick reaction in the immunized children for a longer time and in 1925 found that the period of immunity extended to 10 years for at least 80 per cent of them. These were New York City children. As a rule the same children were not retested in order to avoid the possibility of the Schick test adding its immunizing effect. The long duration of immunization might have been due in some to the added immunizing effect of repeated infection from carriers.In 1918 we began the serious attempt to immunize the whole child population of New York City. This earlier work was concerned mostly with children of school age, as most parents were not yet willing to have the injections given to the babies and very young children.We noted that in a small percentage of the children the injection gave
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