If we vaccinate a man for the first time, we see, at the point of inoculation, no specific changes during the first days, but the vaccinal effect is produced only on the third to the fourth day and reaches its maximum on the eighth to the tenth day. When, however, we repeat the vaccination after several months, we find that there appears, within twenty-four hours, a small local inflammation which afterward disappears rapidly. From this early reaction we can diagnose a previous inoculation if we are not informed of the history.
After careful study of these small skin eruptions in cowpox inoculation, I tried the same method in tuberculosis and found that only individuals who had been infected previously with tuberculosis showed within twenty-four hours a local inflammation after the inoculation with Koch's old tuberculin.
It appeared that this skin reaction was, in principle, identical with Koch's febrile reaction after