The part which healthy carriers of diphtheria bacilli play in the spread of diphtheria has furnished a subject for much study and discussion. Numerous investigators have found culturally and morphologically typical diphtheria bacilli in the throat and nose of from 1 to 4 per cent, of healthy persons. Zingher and Soletsky1 refer to Wilcox and Taylor as finding 4.5 per cent. of carriers among the scarlet fever patients admitted to the Willard Parker Hospital, and in one half, the bacteria were virulent.
While diphtheria bacilli cultivated in cases of clinical diphtheria are practically always virulent, those grown from carriers are often nonvirulent. The general opinion of those who have studied the subject is that the avirulent diphtheria bacilli are harmless, that they never change into the virulent form, and that carriers of such organisms are not a source of danger. Many carriers of diphtheria bacilli rid themselves of the