84 A MANUAL OF BACTERIOLOGY 



latter become filled during the sterilisation. The tubes 

 are inoculated and incubated, and if fermentation occurs 

 the little tube becomes filled with gas (Fig. 16). Einhorn's 

 saccharimeter may also be used (Fig. 17). The tube is 

 filled with the medium, sterilised, inoculated, and in- 



FIG. 16. Durham's 

 fermentation tube. 



FIG. 17. Einhorn's sacchari- 

 meter. 



cubated. 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 : C0 2 ratio may be determined. The 

 most suitable media for fermentation are peptone broth, 

 the acid beef-broth for which has been treated with the 



