Abstract
In testing the degree of immunity set up by vaccination, either with living or with dead tuberclc bacilli, in experimental animals, the lack of uniformity in the selection of the dosage in all probability was responsible to some extent for the discrepancies reported by various investigators.
In calculating such dosage. 3 different methods are in use. Calmette and some of his followers select a dosage based on the calculation that one milligram of moist weight contains 40,000,000 tubercle bacilli. Others in Germany and in this country select their dosage represented in dry weight, using from .001 to .01 milligram, while still others are using the newer direct counting method, which is the most accurate. These various methods have never before been correlated experimentally and no comparison could be made in analyzing the various findings reported in the past. past.
In this report we shall describe the results obtained in an attempt to determine the number of tubercle bacilli present in one milligram of dry weight. The main object is to bring together all these various methods.
A hormgenous type of tubercle bacilli described in the previous paper was used in this experiment. As stated before, this organism grows very readily in the broth and not on the surface like other acid-fast organisms. The suspension was made in physiological salt solution having a pH of 7.8. Phosphate buffer mixtures could not he used for the reason that the salt, being hydroscopic. no complete desiccation could be obtained, and the determinations were not constant. On the other hand, using saline of such a pH, suspensions are easily made and after several filtrations through cotton, approximately 90 per cent represents individual organisms which will not agglutinate spontaneously.
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