424 THE BACILLUS OF ANTHRAX. 
varies considerably in different culture media; and in old cultures 
irregular forms are frequently seen—“ involution forms.” 
Under favorable conditions endogenous spores are developed in 
the long filaments which grow out in artificial culture media. 
These first appear as refractive granules distributed at regular inter- 
vals in the segments of the protoplasm, which gradually disappear 
as the spores are developed; and these are left as oval, highly re- 
fractive bodies, held together in a linear series by the cellular enve- 
lope, and subsequently set free by its dissolution. The germination 
of these reproductive bodies results in the formation of rods and 
spore-bearing filaments like those heretofore described. In this pro- 
cess the spore is first observed to 
lose its brilliancy, from the ab- 
sorption of moisture, a promi- 
nence occurs at one end of the 
oval body, and soon the external 
envelope — exosporium—is rup- 
tured, permitting the softened 
protoplasmic contents enclosed 
in the internal spore membrane 
—endosporium—to escape as a 
short rod, to which the empty 
exosporium sometimes remains 
attached. 
The anthrax bacillus stains 
readily with the aniline colors 
and also by Gram’s method, 
when not left too long in the 
, decolorizing iodine solution. 
; Fig. 99.—Bacillus anthracis, from a culture, show- ,offler’s solution of methylene 
ing formation of spores. X 1,000. (Klein.) ‘ 7 
blue is an especially good stain- 
ing fluid for this as well as for many other bacilli. Bismarck brown 
is well adapted for specimens which are to be photographed, and also 
for permanent preparations, as it is less liable to fade than the blue 
and some other aniline colors. 
Biological Characters.—The anthrax bacillus is aérobic, but 
not strictly so, as is shown by the fact that it grows to the bottom of 
the line of puncture in stab cultures in solid media. It is non-mo- 
tile, and is distinguished by this character from certain common 
bacilli resembling it in morphology—Bacillus subtilis—which were 
frequently confounded with it in the earlier days of bacteriological 
investigation. 
The anthrax bacillus grows in a variety of nutrient media at a 
