APPEARANCES OF CULTURES. 



303 



at 20° C, the same appearances manifest themselves, and later 

 they are accompanied by liquefaction of the gelatin. In gelatin 

 plates, however, instead of the characteristically wreathed ap- 

 pearance at the margin, the colonies sometimes give off radiating 

 spikelets irregularly nodulated, which produce a star-like form. 

 These spikelets are composed of spirally twisted threads. 



From such plates the bacilli can be easily isolated, and the 

 appearances of pure cultures on various media studied. 



Appearances of Cultures. — In bottillon, after twenty-four 

 hours' incubation at 37° C, there is usually the appearance of 

 irregularly spiral threads or flocculi suspended in the liquid or 

 lying at the bottom of the tube. These, on being 

 examined, are seen to be made up of bundles 

 of parallel chains of bacilli. Later, growth is 

 more abundant, and forms a fiocculent mass at 

 the bottom of the fluid. 



In gelatin 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 radi- 

 ate out into the medium from the needle track 

 numberless very fine spikelets which enable the 

 cultures to be easily recognised. These spikelets 

 are longest at the upper part of the needle track 

 (Fig. 109). Not much spreading 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 sloped cul- cui^e of?heInfhrax 

 tares exhibit a thick felted growth, the edges bacillus in peptone- 



r 1 • 1 1 i 1 ,11 • gelatin ; seven days' 



ot which show the wreathed appearance seen m growth, it shows the 

 plate-cultures. Liquefaction here soon ploughs "spiking" and also, 



... - ^ , . at the surface, com- 



a trough m the surface ot the medium. Some- mencing iiquefac- 

 times " spiking " does not take place in gelatin ''°"- Natural size. 

 stab-cultures, only 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 



