Specific Tuberculosis Immunity During Infection *

The variegated picture of tuiberculous infection, both spontaneous in man and experimentally induced in animals, has puzzled students and led to most complicated explanations. Most of the earlier experimental studies were handicapped by the lack of two fundamentals which now appear so essential to a solution. One of these was the primary lack of information on the tubercle bacillus and its virulence or avirulence, and the other was the necessity for an exact interpretation of the quantitative relations between the bacilli and the host as expressed in the evaluation of infection and specific immunity. As long as tuberculin and tuberculin allergy were fitted into the picture of specific immunity, and tuberculin allergy was viewed as synonymous with immunity, progress was hampered because of an experimental phenomenon which did not exist naturally.' However, with a better conception of the avirulence of tubercle bacilli, stressed by Calmette with BCG, and a full recognition of grades of virulence of mammalian bacilli, it became possible to evaluate more exactly the elements involved in specific tubercultosis immunity, to understand its mechanism better, and to determine its part in experimental infection and recovery. It had frequently been noted that certain strains of tubercle bacilli would not infect all of the experimental animals uniformly though used in relatively large amounts, and yet those animals that were infected became definitely tuberculous. These observations were made frequently on guinea-pigs infected with mammalian tu'bercle bacilli to which they were usually acknowledged to be highly suscepti'ble. In earlier studies it was shown that a relative specific tuberculosis immunity is produced readily and consistently by viable avirulent mammalian tubercle bacilli,6 and that this immunity must be produced actively and cannot be transmitted from mother to offspring4 or passively transferred by the injection of blood or plasma. This specific tuberculosis immunity is quantitative and depends on a number of factors,