Vaccinating Properties of Avirulent Dissociates of Five Different Strains of Tubercle Bacilli *

In a period such as the present one, characterized by great advances in chemotherapy, interest in vaccines is at a low ebb. But in the case of tuberculosis, vaccination should probably play a greater part than it has in the experimental assay of new chemical remedies. We have felt that the animals ordinarily used in the laboratory have so little native resistance to the tuberde bacillus that only the most potent drug could be expected to check the course of primary infections with this microorganism. To avoid this dilemma, investigators have frequently resorted to the practice of saturating the tissues with a drug for a period of days or weeks before administering infection. But this procedure has little place in human therapy, and in animals it has engendered false optimism. Bacteriostatic properties may hold the microorganisms in check for days or weeks, but if the animals are allowed to live long enough most drugs are finally eliminated and the tubercle bacilli are then free to multiply and cause disease. We believe that it is much more logical to enhance the low native resistance of guinea-pigs or rabbits to the tubercle bacillus by preliminary vaccination and to test the effect of new remedies during the course of re-infection with a small dose of virulent tuberde bacilli. There are some who will not agree, for they believe that the goal of chemotherapy in human tuberculosis is treatment of the newly discovered, progressive, primary lesion; the chronic lesions, they feel, are too far advanced to benefit greatly. But to them, we would reply that progressive, primary foci that are large enough to be detected in a roentgenogram of the lungs have already become re-infection tuberculosis although endogenous in origin. From time to time, we used all of the accepted methods of vaccinating amals against virulent tuberde bacilli: