388 BACTERIOLOGY. 



usual method — i. e., with Loffler's methylene-blue. 

 There are other organisms present in the mouth-cavity, 

 particularly in the mouths of persons having decayed 

 teeth, the morphology of which is so like that of the 

 bacillus of diphtheria that they might easily be mistaken 

 for that organism if subjected to only the usual method 

 of microscopic examination ; and again, the genuine diph- 

 theria bacillus is sometimes found in the mOuth-cavities 

 of healthy persons in attendance upon diphtheria cases, 

 such persons being at the time insusceptible to the patho- 

 genic activities of the organism. In the vast majority 

 of instances, however, where the clinical condition of 

 the patient justifies a suspicion of diphtheria, a micro- 

 scopic examination alone of the deposit in the throat 

 will serve to confirm or contradict this opinion, and 

 such examinations very frequently reveal the diph- 

 theritic nature, etiologically speaking, of mild condi- 

 tions of the throat which are not associated with grave 

 constitutional manifestations. 



Bacillus diphtherice, discovered microscopically by 

 Klebs, and isolated in pure culture and proved to 

 stand in causal relation to diphtheria by Loffler, can 

 readily be identified by its cultural peculiarities and 

 by its pathogenic activity when introduced into tissues 

 of susceptible animals. In guinea-pigs and kittens the 

 results of its growth are histologically identical with 

 those found in the bodies of human beings who Iiave 

 died of diphtheria. 



When studied in pure culture its morphological and 

 cultural peculiarities are as follows : 



Morphology. — As obtained directly from the diph- 

 theritic deposit in the throat of an individual sick of 

 the disease, it is sometimes comparatively regular in 



