304 ANTHRAX. 



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, how- 

 ever, is useful for studying sporulation. Litmjts milk is feebly 

 acidified, loosely coagulated, and slowly peptonised. 



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. Among the non-pathogenic bacteria the 

 only organism which has similar colonies is the bacillus figurans, 

 and the resemblance is only a distant one. One variety of 

 B. subtilis has been observed to bear a striking general resem- 

 blance to B. anthracis, however. 



The Biology of Bacillus 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 oc- 

 curs 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 



