Diphtheria toxin-antitoxin as an active immunizing agent was discovered in 1913 by Behring and became generally used in the United States from 1914 on. It was found to give immunity to 85 per cent of the subjects who received three 1 cc. injections, and the length of immunity from good preparations was determined by my co-workers and myself as being ten years or more in 80 per cent of the cases.1
In 1924 Zingher and I2 accepted the superiority of Ramon's anatoxin—or, as it is called in this country, the formol toxoid—as compared with toxin-antitoxin. We summed up this superiority by stating that toxoid is (1) more stable, (2) easier to prepare, (3) not dangerous if accidentally frozen, (4) more effective and (5) nonsensitizing. After 1931 administration of toxoid, in two or three doses, gradually supplanted the use of toxin-antitoxin both in Europe and in this country. The