The Fermentation Tube 197 



to insure intimate contact of the CO^ with the alkali. Lastly, 

 before removing the thumb, all the gas is allowed to collect in the 

 closed bra7ich so that none may escape when the thumb is re- 

 moved. If CO, was present, a partial vacuum in the closed 

 branch causes the fluid to rise suddenly when the thumb is 

 removed. After allowing the layer of foam to subside some- 

 what, the glass scale is again applied to the closed branch and 

 the amount of CO, absorbed may thus be measured. In all 

 cultures of this character thus far examined the gas remaining 

 . was explosive in character and probably hydrogen. At any 

 rate wherever hydrogen is referred to hereafter, it simply 

 signifies an explosive gas whose analysis must be left to the 

 chemist. The explosive character of this residue is easily de- 

 monstrated as follows : — The cotton plug is replaced and the 

 gas in the closed branch allowed to flow into the bulb and 

 mix with the air there present. The plug is then removed 

 and a lighted match inserted into the mouth of the bulb. The 

 intensity of the explosion varies with the quantity of air pres- 

 ent in the bulb. 



One difiiculty with the culture fluid employed needs to be 

 mentioned at the outset. It is the presence of a small, but 

 variable amount of glucose in the beef or other meat employed. 

 When only glucose is used the difficulty disappears, but when 

 other sugars are used we are at a loss to know how much of 

 the gas to ascribe to the glucose originally present in the beef 

 infusion or even to know whether the other sugars added are 

 at all attacked by the bacteria. Recently I tested beef broth 

 as it was prepared from time to time in the laboratory by in- 

 oculating fermentation tubes filled with it with a variety of 

 gas-producing bacteria. In the following table the total 

 amount of gas is calculated in percentages of the total volume 

 of the closed branch which is about 20 ccm. The amount of 

 CO2 absorbed by potash is given in percentages of the total 

 volume of gas. The gas remaining is explosive. 



