402 PATHOGENIC MICROORGANISMS 



Tested for its power to form acid from sugars commonly used in 

 differential tests, typhoid bacilli form acid, but no gas, on the mono- 

 saccharides, on mannit, maltose and dextrin, but not on lactose and 

 saccharose. (See Table, p. 44.) 



In the Hiss tube medium (see section on Media, page 133), the 

 typhoid bacillus within eighteen to twenty-four hours produces an even 

 clouding by virtue of its motility, but does not form gas. In contradis- 

 tinction to this, dysentery bacilli grow only along the line of inocula- 



FIG. 88. SURFACE COLONY OF BACILLUS TYPHOSUS ON GELATIN. (After Heim.) 



tion, while bacilli of the colon group move in irregular sky-rocket-like 

 figures away from the stab, at the same time breaking up the medium 

 by the formation of gas-bubbles. Some actively motile colon bacilli 

 cloud the medium, but the ruptures caused by the gas are always 

 evident. 



The differentiation of the typhoid bacillus in pure culture from similar 

 microorganisms by means of its growth upon media has been the sub- 

 ject of many investigations. It is neither practicable nor desirable to 

 enumerate all the various media which have been devised and reported. 



