82 BACTERIOLOGY. 
In order to test the production of gas, a culture 
medium composed of glucose-agar, containing about 
1 per cent. grape sugar, may be used. At the end of 
eight to twelve hours in the incubator (or twenty-four 
hours’ room-temperature) the agar will be seen to be 
full of gas-bubbles or broken up into holes and fissures. 
For the determination of the quantity and kind of 
gas produced by a given micro-organism the fermenta- 
tion tube recommended by Theobald Smith is the best. 
This is a bent tube, constricted greatly at its lowest 
portion (Kichorn’s), supported upon a glass base, as 
shown in Fig. 14. The graduation shown in the 
Fie, 14, 
a LS : 
Fermentation tube left side, ordinary tube on right side. 
upright arm is not essential for ordinary laboratory 
work. The tube is filled with a culture media consist- 
ing of 1 per cent. glucose, peptone bouillon (without 
air-bubbles), and sterilized in the steam sterilizer. It 
is then inoculated with a loopful of a culture of the 
organism in question, and observations taken: 
1. If there is a turbidity produced in the open bulb 
it indicates the presence of an aérobic species; if this 
