APPEARANCES OF CULTURES. 279 



In gelatine stab cultures, the characteristic appearance can 

 be best observed when a low proportion, say 7^ per cent, 

 of gelatine 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 number- 

 less very fine spikelets which enable the cultures to be easily 

 recognised. These spikelets are longest at the upper part 

 of the needle track (Fig. 72). Not much spread takes 

 place on the surface of the gelatine, but here liquefaction 

 commences, and gradually spreads down the stab and out 

 into the medium, till the whole of the gelatine may be 

 liquefied. Gelatine 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 gelatine stab cultures, only little 

 round particles of growth occurring down the needle track, 

 followed by liquefaction. Agar sloped cultures have the 

 appearance of similar cultures in gelatine, though, of course, 

 no liquefaction takes place. 



Blood serum sloped cultures present the same appear- 

 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. 



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, />., multiplication, does not take place below 12 C. 



