BACTERIA IN DIPHTHERIA. 453 
BACILLUS DIPHTHERI. 
First observed by Klebs (1883) in diphtheritic false membranes. 
Isolated in pure cultures and pathogenic power demonstrated by 
Léffler (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- 
tococeus 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 
mM, and from 2 to 3 y/ in length. Iv- 
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 ane: 
of irregular spherical or oval segments. Fig. 112, — Bacillus diphtheria, 
Multiplication occurs by fission only, ‘om * sulture ‘upon blood serum. 
and the bacilli do not grow out into fila- eae ste 
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 Léffler’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 aérobic, non- 
motile, and non-liquefying; it does not form spores. It grows most 
freely in the presence of oxygen, butis also a facultative anaérobie. 
Development occurs in various culture media at a temperature of 
from 20° to 42° C., the most favorable temperature being about 35° C, 
