400 APPLIED BACTERIOLOGY 



on this medium, or were rapidly overgrown by the colon 

 bacillus. The B. coli grew in twenty-four hours, presenting 

 the usual appearance of that organism on acid media ; the 

 B. typhosus was scarcely visible in twenty-four hours, but 

 in forty-eight hours appeared in small, shining, very finely- 

 granulated colonies like little drops of water, which con- 

 trasted strongly with the larger coarsely -granulated 

 brownish colonies of the colon bacillus. The B. coli only 

 acquired the appearance of the typhoid colonies when a 

 great number of the organisms were present, and many, 

 therefore, grew without finding room for their proper 

 development. In plates made with weaker inoculations it 

 is impossible to mistake one bacillus for the other. 



We have used this method with satisfactory results. 

 The colonies of the B. typhosus appear more quickly on this 

 medium than on carbol-gelatine, but otherwise this appears 

 to be the only advantage it possesses. 



Stoddart's Method. — A very promising method for the 

 separation of the typhoid from the colon bacillus has 

 recently been introduced by F. W. Stoddart (TJte Analyst, 

 May, 1897). This process is based upon the difference in 

 the behaviour of the typhoid and coli bacilli when grown 

 upon solid media incubated near their melting-points. 

 The most satisfactory procedure is as follows : An agar- 

 gelatine medium containing 0-5 per cent, of agar and 5 per 

 cent, of gelatine, with the usual proportions of peptone and 

 salt, is made, with all precautions to avoid loss of moisture 

 during preparation. The reaction of the medium must be 

 distinctly alkaline. The agar-gelatine is poured into flat- 

 bottomed flasks or dishes to a depth of about 5 m.m., 

 sterilised, and allowed to cool slowly in the steriliser, so as 

 to avoid the exudation of moisture on the surface. The 

 plates or flasks, which should not be more than a few days 

 old, are then inoculated with a charged needle, and are 



