THE SCHICK TEST.
A few years ago a very simple test was discovered to tell whether a person could or could not catch diphtheria. This is known as the Schick test. It consists in injecting a few drops of a prepared diphtheria toxin into the skin and then watching whether a characteristic red spot appears where the injection was made. If such a spot does not appear within two or three days it shows that the person can not catch diphtheria.