STUDIES ON TUBERCULIN SENSITIVITY AND IMMUNITY IN GUINEA‐PIGS INDUCED BY VACCINATION WITH VARYING DOSES OF BCG VACCINE

SUMMARY Six groups of guinea‐pigs, each consisting of 20 animals, were vaccinated with 10−6, 10−5, 10−4, 10−3, 10−2 and 10−1 mg BCG vaccine, half the animals in each group being vaccinated intraperitoneally and the other half subcutaneously. Forty‐two days later the animals were tested with tuberculin, and after a further 8 days challenged intravenously with 10−6 mg virulent bovine tubercle bacilli. The animals were allowed to live until death occurred spontaneously. The survival time was used as the measure of the immune effect. Results. 1. Both tuberculin sensitivity and immunity depend on the dose of vaccine used, but both reactions appear to remain constant when the dose is increased beyond 10−3 mg. 2. The lowest dose of vaccine which can cause tuberculin sensitivity and immunity in a large number of treated animals is 10−5 mg. 3. Though the survival time is prolonged by use of increasing doses of vaccine, there is no pronounced difference in the immunity in the 10−1 group and in the tuberculin positive animals in the 10−5 group. 4. Under the experimental conditions in this study, tuberculin sensitivity is always accompanied by immunity. 5. For a given dose there is no parallelism between the size of the tuberculin reaction and the extent of immunity. 6. There is no difference betwen the survival times of the tuberculin negative animals in the vaccinated groups and those of the control animals. 7. The acquired immunity is just as great, whether the animals are vaccinated intraperitoneally or subcutaneously. The tuberculin reactions are slightly bigger in the animals vaccinated intraperitoneally.