258 



PATHOGENIC BACTERIA. 



minute portion of the feces is broken up with a platinum 

 loop and stirred in the tube of melted gelatin ; a drop 

 from this dilution is transferred to the second tube, a 

 drop from it to a third, and then the contents of each 

 tube are poured upon a sterile plate or into a Petri dish, 



FIG. 75. Bacillus typhi abdominalis : superficial colony two days old, as 

 seen upon the surface of a gelatin plate; x 20 (Heim). 



FIG. 76. Bacillus coli communis : superficial colony two days old upon a 

 gelatin plate; x 21 (Heim). 



or rolled, according to Esmarch's plan, in the manner 

 already described. The carbolic acid present in these 

 cases prevents the great mass of saprophytes from de- 

 veloping, but allows the perfect development of the 



