128 BACTERIOLOGICAL LABORATORY TECHNIC 



The property of converting sugar into acids and gases is best 

 studied in fermentation tubes. 



Into sterile fermentation tubes bouillon containing sugar is run, 

 these are plugged and sterilized. They may be inoculated with 

 bacteria and if gas production occurs it is quickly manifested in 

 the closed arm. The component gases may be studied and the 

 various properties determined. This gas ratio is of use in identi- 



FIG. 33. Fermentation tube. (Williams.) 



fying various bacteria and differentiating them. The closed arm 

 of the tube being shut off from free air by the amount of bouillon 

 in the open arm is practically an anaerobic tube and is employed 

 for this purpose. Bacteria that grow only in the closed arm are 

 considered anaerobes. By inoculating a gelatine tube with bac- 

 teria while it is melted and then letting it solidify, previously 

 shaking the tube vigorously, gas formation will be speedily mani- 



