BIOLOGY OF THE B. ANTHRACIS 335 



to be made up of bundles of parallel chains of bacilli. Later, 

 irmxvth is more abundant, and forms a flocculent mass at the 

 bottom of the fluid. 



In yelatin stab cultures, the characteristic appearance can be 

 best observed when a low proportion, say 7J per cent., of gelatin 

 is present, and when the tube is directly inoculated from 

 anthrax blood. In about two days there radiate out into the 

 medium from the needle track numberless very fine spikelets 

 which enable the cultures to be easily recognised. These spike- 

 lets are longest at the upper part of the needle track (Fig. 101). 

 Not much spread takes place on the surface of the gelatin, but 

 here liquefaction commences, and gradually spreads down the 

 stab and out into the medium, till the whole of the 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 tract, followed by liquefaction. 

 As has been shown by Rd. 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. The occurrence of capsulation of the bacilli in such 

 cultures has been described. 



On potatoes there occurs a thick felted white mass of bacilli 

 showing no special characters. Such a growth, however, is use- 

 ful 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 0. Growth, 

 i.e. multiplication, does not take place below 12 C. nor above 

 45 C. In the spore-free condition the bacilli have comparatively 

 low powers of iv<i<t;mce. They do not stand long exposure to 

 60 C., and if kept at ordinary temperature in the dry condition 



