Owing to the frequency of diphtheria and the comparative ease of making bacteriologic examinations in this disease, the laboratory has been freely used as an aid in its diagnosis and management, so that the bacteriology may be considered one of the best developed subjects in the domain of bacteriology.
The morphologic, biologic and tinctorial qualities of diphtheria bacilli are so distinctive that with comparatively little experience they are readily detected in properly made cultures, and if diphtheria bacilli were to be found on mucous membranes only in diphtheria and disappeared in a reasonable length of time after the clinical evidences of infection had disappeared, nothing would be simpler or more satisfactory than the bacteriologic diagnosis of the majority of these infections.
From a practical standpoint, however, the bacteriologic diagnosis of diphtheria is greatly complicated by reason of the fact that many persons harbor diphtheria-like bacilli in the mucous membranes, particularly