MORPHOLOGY. 327 



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 microscopic 

 examination only; and again, the genuine diphtheria 

 bacillus is sometimes found in the mouth cavities of 

 healthy persons in attendance upon diphtheria cases, 

 who were at the time insusceptible to the pathogenic 

 activities of the organism. In the vast majority of 

 instances, however, where the clinical condition of the 

 patient justifies a suspicion of diphtheria, a microscopic 

 examination alone of the deposit in the throat will serve 

 to confirm or contradict this opinion. 



Bacillus diphtheria, discovered microscopically by 

 Klebs, and isolated in pure culture and proved to 

 stand in causal relation to diphtheria by Loeffler, 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 have 

 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 

 shape, appearing as straight or slightly curved rods with 

 more or less pointed ends. More frequently, however, 

 spindle and club shapes occur, and not rarely many of 

 these rods take up the stain irregularly; in some of 

 them very deeply stained, round or oval points can be 

 detected. 



When cultures are examined microscopically it is 



