458 



PATHOGENIC BACTERIA. 



anilin dyes, and can be beautifully demonstrated in the 

 tissues by Gram's method and by Weigert's fibrin method. 

 Picro-carmin, followed by Grain's method, gives a beauti- 

 ful, clear picture. The spores can be stained with carbol- 

 fuchsin, the bacilli decolorized with a very weak acid and 

 then counter-stained with a watery solution of methyl blue. 

 Upon the surface of gelatin plate-cultures the bacillus 

 forms beautiful and highly characteristic colonies (Fig. 

 108). To the naked eye they appear first as minute 



Fig. 108. — Bacillus anthracis: colony upon a gelatin plate ; x ioo (Frankel and 



Pfeiffer). 



round whitish dots occurring upon the surface, and caus- 

 ing liquefaction of the gelatin as they increase in size. 

 Under the microscope they can be seen in the gelatin as 

 egg-shaped, slightly brownish granular bodies, not attain- 

 ing their full development except upon the surface, where 

 they spread out into flat, irregular, transparent growths 

 bearing a partial resemblance to tufts of curled wool. 

 From a tangled centre large numbers of curls extend, 

 each made up of parallel threads of bacilli. As soon as 

 the colony attains any considerable size liquefaction be- 

 gins. These colonies make beautiful adhesive prepara- 

 tions. If a perfectly clean cover-glass be passed once 



