304 ANTHRAX 



little round particles of growth occurring down the needle track, 

 followed by liquefaction. As has been shown by Richard 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. 



Blood serum sloped cultures present the same appearances 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 recognised by its 

 microscopic appearance, by its growth on agar or gelatin plates, 

 and by its growth in gelatin stab cultures. The growth on 

 plates is specially characteristic, and is simulated by no other 

 pathogenic organism. 



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 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 about the same 

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

 107). The latter gradually loses its staining capacities and 

 finally disappears. The spore thus lies free as* 1 an oval highly 



