338 ANTHKAX 



gelatin may be liquefied. Gelatin slope cultures exhibit a thick 

 felted growth, the edges of which show the wreathed appearance 

 seen in plate cultures. Liquefaction here soon ploughs a trough 

 in the surface of the medium. Sometimes " spiking " does not 

 take place in gelatin stab cultures, only little round particles of 

 growth occurring down the needle track, followe'd by liquefaction. 

 As has been shown by Ed. Muir, this property of spiking can be 

 restored by growing the bacillus for twenty-four hours on blood- 

 agar at 37° C. Agar sloped cultures have the appearance of 

 similar cultures in gelatin, though, of course, no liquefaction 

 takes place. On these sporulation can be readily developed. 

 The organism grows readily on blood serum and potato, but the 

 cultures show no special characteristics. 



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

 bacillus anthracis grows best at a temperature of 35° C. 

 Multiplication does not take place below 12° C. nor 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 temperature 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 accord- 

 ingly destroyed in the stomachs of healthy animals. They are 

 also soon killed in the process of putrefaction. They can, how- 

 ever, 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 gelatin always commences at the 

 surface and spreads downwards. Growth is more rapid in the 

 presence of oxygen, and spore-formation 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 ; this gradually 

 increases in size until it forms an oval body of about the same 

 thickness as the bacillus lying in the bacillary protoplasm (Fig. 

 101). The latter gradually loses its staining capacities and 

 finally disappears. The spore thus lies free as an oval highly 

 refractile body which does not stain by ordinary methods, but 

 which can be easily stained by the special methods described for 

 such a purpose (p. 106). When the spore is again about to 

 assume the bacillary form the capsule is apparently absorbed, 

 and the protoplasm within grows out, taking on the ordinary 

 rod-shaped form. 



