Since August, 1924, we have been testing all of the employed personnel, including nurses and physicians, who have come to the Cleveland City Hospital for training in the contagious disease department. Dick tests have been made under various conditions, and we have found that for all practical purposes a control test may be made with boiled toxin (boiled for twenty minutes), which will not cause any pseudoreaction persisting after twenty-four hours, and that, in general, persons with negative Dick tests have negative reactions for at least eighteen months.
ACTIVE IMMUNITY
The next series of experiments, which ran concurrently with those described in the first paper, were made to find out how soon active immunity was established after immunization had begun. The toxins used in the experiments for the first year were received from the Dicks; after that they were received from commercial sources.Experiment 1.—This was made to ascertain whether