Immunity results obtained in school children with diphtheria toxoid (modified toxin) and with 1/10 L+ mixtures of toxin-antitoxin.

Excellent immunity results obtained with 3 L+ mixtures of toxin-antitoxin, which were originally underneutralized but had become on standing neutral for the guinea pig, indicated that the toxoid into which the free or slightly bound toxin had been changed was effective as an immunizing agent. Dissociation of the mixture into toxin and antitoxin is probably not of much importance as a factor in active immunization since mixtures that are overneutralized or just neutral when freshly prepared do not give good immunity results. Three doses of a freshly diluted toxin were found to immunize only 33 to 41 per cent of susceptible children, while three doses for a dilution of an old, deteriorated toxin, of which 1.0 cc. caused paralysis in the guinea pig, immunized 70 per cent of children. The value of toxoid for immunization purposes has been confirmed by using modified diphtheria toxin, treated by the addition of 0.1 per cent formalin according to the suggestion of Glenny and Hopkins. In four schools in which a preparation of toxoid has been used the following very significant results were obtained at the end of three months: The toxoid was made from a diphtheria toxin which at the time of preparation had an M.L.D. of 0.001 cc. Two years later the M.L.D. was 0.01 cc. and the L+ 0.32 cc. 0.1 per cent formalin was added (1 cc. commercial formalin to 1000 cc. of toxin) and the preparation kcpt in the thermostat for five weeks. At the end of this time the M.L.D. had dropped to 1.5 cc. and the L+ to 3.5 cc. The toxoid was diluted 1 part in 20 parts of saline (5 per cent) for P. S. No. 103 and 1 in 14 (7.5 per cent) for P. S. Nos. 83, 19, and 14. In other schools that are being retested now the dilution of the toxoid was 1 in 10 (10 per cent).