Standardization of typhoid vaccine by photometric methods.

Abstract

Owing to an inquiry from Dr. Joseph W. Smith, Jr., of the Army Medical School, as to the suitability of the photomètre to estimate the strength of bacterial suspensions, a series of investigations were undertaken. Since the completion of this work, Dr. Smith 1 has published two articles on this general subject. From the result of our own experiments we are in accord with his critical statements in regard to the accuracy of the counts made by the Wright's method in standardizing bacterial vaccines. Further, we would emphasize the error introduced in laboratories employing women, by their use of the normal erythrocyte count for men, rather than the actual erythrocyte count for the worker. Where the vaccine prepared is an autogenous one the errors are of lesser importance. However, with stock vaccines for administration to several individuals either for treatment or for immunization, the need of at least reasonable precision in standardization is generally recognized.

The present communication is based on the examination of ten bacterial suspensions made from different cultures of the typhoid bacillus, the strength of the suspension being estimated first, by the microscopic counting method of Wright on dry film, second, by the reading for the absorption of light in the photomètre, and third, by the reading for the diffusion of light in th'e same instrument. For the count, blood slides were made and counted, a dilution of 5,000 million organisms per 1 cc. of vaccine, prepared in accordance with the average of the counts, and later an additional check introduced, by counting the final 5,000 million dilution in similar manner. The stock solution was stored in a special bottle devised to prevent contamination, and permit easy removal of any desired amount, without opening the bottle.