BACILLUS OF TYPHOID FEVER 



401 



identification. On it typhoid bacilli, after twenty-four to forty-eight 

 hours, produce a hardly visible growth, evident to the naked eye 

 only by a slight moist glistening, an appearance which is in marked 

 contrast to the grayish-yellow or even brown and abundant growth 

 of the colon bacilli. If the potato medium is rendered neutral or 

 alkaline, this distinction disappears, the typhoid bacillus growing 

 more abundantly. 



In milk, typhoid bacilli do not produce coagulation. In litmus-milk, 

 during the first twenty-four hours, the color is changed to a reddish or 

 violet tinge by the formation of acid from the small quantities of mono- 



'-t^:^ li"'-- 



Fig. 87. — ^Bacillus typhosus, showing flageUa. (After Frankel and Pfeiffer.) 



saccharid present. Later the color becoines deep blue from the forma- 

 tion of alkali. 



In Dunham's pejyton solution no indol is produced. According to 

 Peckham, however, continuous cultivation in rich pepton media may 

 lead to eventual indol formation by typhoid bacilli. This fact appears 

 to have no bearing on the value of the indol test, as indol is never formed 

 under the usual cultural conditions. 



In dextrose, mannite, lactose, and saccharose broth, the typhoid bacil- 

 lus produces no gas. A comparative summary of the action of other 

 bacilli of this group in these sugar media will be given in the final dif- 

 ferential table on page 443. 



