BACTERIA IN DIPHTHERIA. 375 



47. BACILLUS DIPHTHERIA. 



First observed by Klebs (1883) in diphtheritic false membranes. 

 Isolated in pure cultures and pathogenic power demonstrated by 

 Loffler (1884). 



Found in diphtheritic pseudo-membranes, and especially in the 

 deeper portions, intermingled with numerous cellular elements; while 

 the superficial layers of the membrane commonly contain but few 

 cells or bacilli, or are invaded by other species, especially by Strep- 

 tococcus pyogenes. The bacilli are not found in the affected mucous 

 membrane, or in sections from the internal organs in fatal cases of 

 this disease. 



Morphology. Rods, straight or slightly curved, with rounded 

 ends, having a diameter of 0.5 to 0.8 

 jt, and from 2 to 3 IJL in length. Ir- 

 regular forms are very common, and, 

 indeed, are characteristic of this bacil- 

 lus. In the same culture, and especially 

 in an unfavorable culture medium, very 

 great differences in form and dimen- 

 sions may be observed ; one or both ends 

 may appear swollen, or the central por- 

 tion may be notably thicker than the 

 extremities, or the rod may be made up 



of irregular spherical or oval segments. FIG. 114. Bacillus diphtheria*, 

 Multiplication occurs by fission only, SLtJSlS 



aild the bacilli do not grOW Out into fila- (Frankel and Pfeiffer.) 



ments. 



In unstained preparations certain portions of the rod, and espe- 

 cially the extremities, are observed to be more highly refractive than 

 the remaining portion ; and in stained preparations these portions 

 are seen to be most deeply colored. The diphtheria bacillus may be 

 stained by the use of Loffler's alkaline solution of methylene blue, 

 but is not so readily stained with some of the other aniline colors 

 commonly employed. It stains also by Gram's method. For the 

 demonstration of the bacillus in sections of diphtheritic membrane 

 " nothing can surpass in brilliancy and sharp differentiation sections 

 stained doubly by the modified Weigert's fibrin stain and picro-car- 

 mine" (Welch and Abbott). 



Biological Characters. The diphtheria bacillus is aerobic, non- 

 motile, and non-liquefying; it does not form spores. It grows most 

 freely in the presence of oxygen, but is also a facultative anaerobic. 



Development occurs in various culture media at a temperature of 

 from 20 to 42 C., the most favorable temperature being about 35 C. 



