The Use of the Chick in Titration of Diphtheria Antitoxin

Abstract

Twelve commercial diphtheria antitoxins have been titrated in eight day old White Rock chicks. Repeated tests give unit values with no more than 3% variation. Such a titration was also used for small amounts of antitoxin in the serum of guinea pigs immunized with toxoids. Twelve toxoids were studied in this way. Both the commercial antitoxins and the sera from toxoid-immunized animals were also titrated in guinea pigs by the official guinea pig test recommended by the Laboratory of Biologics Control of the National Institutes of Health. The unit values obtained by the two methods were approximately the same. Evidence to support the validity of these titrations in chicks is found in the straight lines obtained when the amount of toxin and antitoxin neutralized at various unit levels are plotted on log-log paper. Under circumstances where large numbers of tests are required and satisfactory guinea pigs are difficult to obtain, the chick test affords a convenient and reliable tool for use in the study of diphtheria.