Some Observations on the Method of Preparing Old Tuberculin and on the Titration of Its Potency

Abstract

1. On the abilities of producing tuberculin from tubercle bacilli, four strains showed no remarkable difference in regard to the period of cultivation. But there may be some difference in the time chosen for the optimum production of tuberculin. 2. Tuberculins prepared after modifying the pH of culture filtrates over 4.2 showed no variation in potencies. 3. Among various condensation methods, such as evaporation at 70°-80℃ and at 100℃, evaporation under reduced pressure at 45°-55℃ and ultrafiltration through a collodion membrane, condensation by mild evaporation at 70°-80℃ led to retention of the highest activity. 4. For measuring potencies of tuberculin, skin reactions should be tested on tuberculous guinea pigs during the earlier period of infection as well as during the later period. 5. The range of dilutions of tuberculin in testing potencies is more suitable in lower dilutions (1 : 10 to 1 : 1000) than in higher dilutions (1 : 2000 to 1 : 4000) of the late League of Nations.