INTESTINAL OR COLON-TYPHpID GROUP 



279 



is now generally conceded to be the cause of typhoid fever, al- 

 though the experimental animals cannot ordinarily be infected. 



Distribution. Typhoid fever is widely distributed throughout 

 temperate and tropical countries. It is constantly present, fre- 

 quently in epidemic form, in the United States. 



Morphology. Bacillus typhosus is a short, plump rod, usually 

 varying between 0.5 and 0.8 (J- in diameter, and 1 to 3 ^ in length. 

 It is motile by means of numerous flagella. It does not produce 

 capsules or spores. It stains readily with aqueous anilin dyes. 

 Granular staining is some- 

 times observed, although the 

 cells usually stain uniformly. 

 It is gram-negative. 



Isolation and Culture. 

 The desirability of isolating 

 B. typhosus from contamin- 

 ated water has led to the 

 development of many media 

 in an effort to accomplish 

 this. A quantitative esti- 

 mation of the typhoid bacil- 

 lus from such sources does 



not seem to be practicable, 



Pig. llo. Bacillus typhosus, clump in 



but the qualitative deter- a sec tion of a spleen (Frankel and 

 mination of presence may be Pfeiffer). 

 carried out. The methods 



used are to inhibit the growth of the purely saprophytic organ- 

 isms present by the use of antiseptic substances, such as mala- 

 chite green, caffeine, and crystal violet, and to incubate such 

 media at blood-heat. These media do not inhibit, in general, 

 the growth of either B. typhosus or B. coli, and dependence is 

 placed upon differences in colony characters and media reactions 

 to separate them in subsequent plating. 



The colonies upon gelatin are somewhat smaller and more 

 delicate than those of the B. coli. This organism was originally 

 described as producing a thin, " invisible growth " upon potato. 

 This is true upon potato with an acid reaction, but upon alkaline 

 or neutral potato the growth is relatively abundant. 



