642 PATHOGENIC MICROORGANISMS 



of the Proteus group. It forms indol and produces acid and gas on 

 dextrose and saccharose, but one of its chief characteristics is its slight 

 action on lactose. Jordan states as one of its chief characteristics the 

 relatively large proportion of C02 formed as compared with hydrogen, 

 the ratio being in some cases as high as 5 to 1. Kendall, Day and 

 Walker 27 have observed the same thing. The same investigators 

 state that after three days' growth, even sugar broths become alkalin, 

 owing to protein decomposition. 



Recently certain stains of Proteus have become important because 

 of their apparently specific agglutination in Typhus Serum (Weil- 

 Felix Reaction). See chapter on Typhus. 



Were we following a purely biological order of presentation, we 

 should now proceed to a description of the organisms belonging to the 

 so-called Mucosus Capsulatus or Friedlander group. These bacilli 

 are closely related to the Colon type, more particularly to the B. aero- 

 genes variety, and have been regarded by some observers, notably 

 Fitzgerald, as perhaps representing members of the Colon group which 

 have acquired capsulation and virulence. In practice, however, these 

 bacteria are rarely encountered under conditions where differentiation 

 from Colon bacilli is necessary, and their heavy mucoid colonies and 

 capsulated morphology renders their recognition relatively easy. It 

 will be better, therefore, from the point of view of practical discussion, 

 to proceed directly to the study of organisms of the typhoid and dysen- 

 tery groups, since these are the ones which in medical and sanitary 

 bacteriology, are associated in the human body, in water and sewage 

 with members of the Colon group and which, therefore, present the most 

 frequent differential problems. 



27 Kendall, Day and Walker, Jour. Amer. Chem. Soc., 1913, 35. 



