80 A MANUAL OF BACTERIOLOGY 



Trisaccharides (yielding three other sugars by hydrolysis: 

 Ci 8 . . .): Raffinose. 



Polysaccharides [(C 6 Hi 5 )n] : Starch, dextrin, inulin. 



Glucosides (yielding glucose on hydrolysis by acid or enzyme) : 

 Salicin, amygdalin, coniferin, arbutin, sesculin, iridin, etc. 



Milk may show an acid or an alkaline reaction, or the former 

 changing to the latter, with or without curdling, and if curdled, 

 the clot may or may not be digested. 



For the detection of fermentation and gas production, 

 stab cultures in agar or shake cultures in gelatin may 

 be employed, a sufficiency (1 per cent, or so) of the parti- 

 cular fermentable substance having been added to the 

 medium. For a shake culture a tube of gelatin is melted 

 at a low temperature, inoculated with the organism, 

 and allowed to solidify in the upright position ; the 

 organism is thereby distributed throughout the medium. 

 Fermentation with gas production is indicated by the 

 presence of gas bubbles (see Fig. 43) or even by the 

 disruption of the medium. To demonstrate glucose 

 fermentation, ordinary nutrient gelatin is frequently 

 employed for the " shake," but it must be meat, and not 

 Lemco, gelatin. Durham's fermentation tubes are very 

 convenient for showing fermentation. These are test- 

 tubes containing suitable fluid media into which small 

 glass tubes closed at the upper end are placed ; the 

 latter become filled during the sterilisation. The tubes 

 are inoculated and incubated, and if gas-formation occurs 

 some of the gas is caught in the little tube (Fig. 11). 

 Einhorn's saccharimeter may also be used (Fig. 12). The 

 tube is filled with the medium, sterilised, inoculated, and 

 incubated. Any gas produced collects in the closed limb 

 of the tube. When the amount of gas ceases to increase, 

 a little strong caustic potash solution may be added ; this 

 absorbs the C0 2 , the residue probably being hydrogen, 

 and thus the H : CO 2 ratio may be determined. The 

 most suitable media for fermentation are peptone broth, 



