300 ANTHRAX. 



ances as those on agar. The margin of the surface growth 

 on any of the solid media shows the characteristic wreathing 

 seen in plate colonies. 



On potatoes there occurs a thick felted white mass of 

 bacilli showing no special characters. Such a growth, 

 however, is useful for studying sporulation. 



The anthrax bacillus will thus grow readily on any of 

 the ordinary media. It can usually be sufficiently recog- 

 nised by its microscopic appearance, by its growth on agar 

 or gelatine plates, and by its growth in gelatine stab cul- 

 tures. The growth on plates is specially characteristic, and 

 is simulated by no other pathogenic organism. Among 

 the non-pathogenic bacteria the only organism which has 

 similar colonies is the bacillus figurans, and the resemblance 

 is only a distant one. 



The Biology of the B. Anthracis. Koch found that the 

 bacillus anthracis grows best at a temperature of 35 C. 

 Growth, i.e., multiplication, does not take place below 12 C. 

 or above 45 C. In the spore-free condition the bacilli 

 have comparatively low powers of resistance. They do not 

 stand long exposure to 60 C., and if kept at ordinary tem- 

 perature in the dry condition they are usually found to be 

 dead after a few days. The action of the gastric juice is 

 rapidly fatal to them, and they are accordingly destroyed in 

 the stomachs of healthy animals. They are also soon 

 killed in the process of putrefaction. They can, however, 

 be cooled below the freezing-point without dying. The 

 bacillus can grow without oxygen, but some of its vital 

 functions are best carried on in the presence of this gas. 

 Thus in anthrax cultures the liquefaction of gelatine always 

 commences at the surface and spreads downwards. Growth 

 is more rapid in the presence of oxygen, and spore forma- 

 tion does not occur in its absence. The organism may 

 be classed as a facultative anaerobe. 



Sporulation. Under certain circumstances sporulation 

 occurs in anthrax bacilli. The morphological appearances 

 are of the ordinary kind. A little highly-refractile speck 

 appears in the protoplasm about the centre of the bacillus ; 



