Methods of Determination of Pathogenic Microbes. 137 



similar variations. As these media do not become 

 fluidified like gelatin, they are better adapted for 

 studj'ing the evolution of the germ colonies. 



Some germs give characteristic cultures in certain 

 media. Glanders, for instance, upon potato, gives a 

 slimy looking culture with chocolate brown margins; 

 charbon, sown in gelatin by " stab " inoculation, 

 grows in the form of a test tube brush, liquefying 

 the nutritive medium. 



Cultures in bouillon are no less variable. Some- 

 times we observe a uniform turbidity which is slowly 

 deposited, in other cases clots of progressively in- 

 creasing dimensions floating in the liquid; sometimes 

 a flocculent coherent mass looking like a piece of sat- 

 urated wadding suspended in the liquid (charbon) ; 

 in still other cases, finally, we see agglomerated colo- 

 nies floating on the surface of the bouillon like leaves 

 of the water-lily upon water (farcy of cattle). These 

 various appearances evidently depend upon the mode 

 of association of the germs of which the culture is 

 composed. The long filaments take the form of tufts 

 of hair ; chains of micrococci that of small pellets ; 

 isolated micrococci produce a uniform turbidity of 

 the fluid. 



Germs may change the color of the culture media ; 

 such changes are sometimes sufficient to distinguish 

 these germs: blue pus. Anaerobic germs often give 

 rise to a disengagement of gases more or less oflensive, 

 recalling those of putrefaction. 



Chemical characters. — The chemical reactions to 

 which the multiplication of germs gives rise natu- 

 rally vary according to the germs concerned; they 

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