10 



TABLE II. RELATION OF HANGING DROP AND SEMI-SOLID AGAR FOR 



DETERMINATION OF MOTILITY. 



(After Chen and Rettger, 1920) 



Levine, however, in a study of 151 strains of the aerogenes-cloacae 

 group, found an excellent correlation between motility, as determined in 

 semi-solid medium, gelatin liquefaction and starch fermentation. Thus 

 of 89 motile organisms 81 (91.0%) liquefied gelatin and only 4 (4.5%) 

 fermented starch; whereas among 62 non-motile organisms only 2 (3.2%) 

 liquefied gelatin while 61 (98.5%) fermented starch. A test which cor- 

 relates so well with other characters is probably of differential value, and, 

 although it is not recommended at present for routine work, it may be of 

 significance and should be included in investigational studies. 



MacConkey recommends that motility be observed in six hour cul- 

 tures using dark field illumination. Castellani and Chalmers also employ 

 motility as an important differential criterion. 



Fermentation of carbohydrates. The carbohydrates which have 

 been most commonly employed in the study of the colon group are listed 

 below: 



Monosaccharids. Glucose, levulose, and galactose. 



Disaccharids. Lactose, sucrose, and maltose. 



Trisaccharid. Raffinose. 



Polysaccharids. Starch, inulin, and glycogen. 



Alcohols. Glycerol, mannitol, dulcitol, and adonitol. 



Glucoside. Salicin. 



The media for fermentation tests generally consist of peptone water or 

 broth containing one percent of the test substance. Incubation is at the 

 body temperature for 48 hours and a positive reaction is indicated by 

 gas production. If desired, litmus, brom cresol purple, neutral red, or 

 the Andrade indicator may be added to the medium to observe acid for- 

 mation. 



Kligler suggests that quantitive acid-production be substituted for 

 gas-formation as an index of fermentation. He points out that in stand- 

 ard meat-infusion sugar-freed carbohydrate broth media there is a rather 

 sharp dividing line between acid-producers and nonacid-producers at 1.5 

 percent normal acid and that quantitive gas-production is variable and 

 unreliable. Although quantitive gas-formation as ordinarly determined in 

 the Smith or Durham tube is markedly inconstant and therefore of little 



