The Buffered Diluent for Schick Toxin.

Abstract

The instability of diphtheria toxin in diluted state has always presented obstacles to the preparation of outfits for the Schick test. It has been the custom to supply a small amount of undiluted toxin (or toxin in a small amount of glycerin) in one container and the required amount of saline diluent in another container, which required the mixing of toxin and diluent by the physician at the time of performing the Schick tests. A ready-made dilution of toxin which would retain its toxicity under the varying conditions to which Schick outfits are usually subjected would make for lower cost of manufacture, greater convenience and greater accuracy of the test itself.

A buffered diluent described by Glenny, Pope and Waddington 1 might make such a procedure feasible. They found that most diphtheria toxins diluted in the buffer maintained their toxicity for 6 weeks at room temperature and for 6 months or more at 0° C. We began a series of experiments to check their results, using a toxin which was being employed routinely in Schick test outfits.

The toxin was prepared from veal infusion made sugar free with B. coli, containing 2% Difco Proteose Peptone, 0.5% sodium chloride and having a pH of 7.4 after autoclaving 30 minutes at 120° C. The “Park-Williams No. 8” strain was used and the toxin harvested after incubation at 35° C. for 5 days. The toxin was 6 years old at the time of the experiments and had an M.L.D. of 0.015 cc. Two M.L.D. plus 20% excess was accurately measured into capillary tubes and the contents diluted in 10 cc. vials of isotonic salt solution containing 0.4% phenol or in 10 cc. vials of the buffered diluent (pH 8.1) prepared according to the Glenny, Pope and Waddington directions.