322 MICROBIOLOGY 



Gelatin. This medium shows colonies in from 24 to 36 

 hours at room temperature appearing as small, transparent, 

 convex, round, or occasionally leaf-shaped colonies. The 

 growth does not spread on the surface as is the usual habit of 

 the colon bacillus. The gelatin is not liquefied. In stab cul- 

 tures the growth extends along the entire length of the needle 

 culture. With age the colonies become more opaque. 



Potato. The growth on potato is somewhat distinctive. 

 It was recommended by Gaffky as one of the means of identi- 

 fication. In from 24 to 48 hours the growth is hardly visible 

 to the unaided eye. Sometimes this growth can not be seen 

 except w r ith the hand lens. If the potatoes are neutralized or 

 made slightly alkaline the growth is much more abundant. 



Bouillon. In bouillon the growth is rapid, imparting an 

 even cloudiness throughout the liquid. The extent of the 

 'cloudiness varies somewhat. In some cultures the liquid 

 becomes almost turbid. Rarely a pellicle is formed. In 

 bouillon containing \% dextrose, the liquid becomes acid but 

 gas is not formed. This is true of levulose and mannite. In 

 bouillon containing lactose and saccharose, the culture remains 

 alkaline. 



Milk. No appreciable change is produced in milk, al- 

 though it is a good culture medium for this organism. In 

 litmus milk the color becomes slightly reddish at first, due to 

 the small amount of monnosaccharid present. Later the 

 medium becomes deep blue due to the formation of alkali. 

 The milk, however, is not saponified as in the case of B. sui- 

 pestifer. 



Life conditions and properties. B. typhosus is an aerobe 

 and facultative anaerobe. It grows best at a temperature of 

 about 37 C. and in a neutral medium. It produces a toxin 

 but there seems to be a difference of opinion as to whether the 

 poisons produced by this organism are so-called endotoxins 

 only or whether they are in part composed of soluble toxins 

 comparable to those of diphtheria and tetanus. Besredka 3 



3 Besredka. Ann. de 1'Inst. Pasteur, Vol. XIX (1905) p. 477. Also 

 Vol. XX (1906) p. 149. 



