The Fermentation Tube 195 



In spite of the fact that I called attention to this matter three 

 years ago'' by describing a procedure for determining the pro- 

 duction of gas as simple as the ordinary cultivation of bacteria, 

 this procedure has not been generally adopted largely because 

 the fermentation tube itself seems to be looked upon as some- 

 thing beyond the range of the ordinar}^ bacteriological outfit. 



In referring to gas formation writers have been in the habit 

 of calling attention to the gas bubbles which make their ap- 

 pearance under certain conditions in stick {Stick-) cultures in 

 gelatin and agar as well as in inclined or ' ' slant ' ' cultures of 

 agar if there is condensation water present. These bubbles 

 appear in the depths of the gelatin, one or more days after 

 inoculation, as flat, lenticular spaces cleaving the jelly in one 

 or more directions. In agar stick cultures, kept at 37° C. 

 they appear frequently within 24 hours after inoculation with- 

 in the depths of the agar jelly. In slant cultures they are 

 usually found between the agar and the sides of the tube, im- 

 prisoned there by the condensation water which fills the gap 

 between the slightly retracted agar and the glass. These bub- 

 bles depend for their presence on two things: i , The capacity 

 of the particular species for fermenting glucose with the pro- 

 duction of gas ; and, 2, The presence of glucose in the meat 

 used in the preparation of the nutrient gelatin or agar. As 

 I shall point out farther on the meat infusion is in some cases 

 entirely free from such fermenting substance and if accidently 

 used the bubbles will not appear. This test is therefore unre- 

 liable. A much better method and one which should not be 

 neglected if the fermentation tube is not at hand is to add a 

 definite quantity of glucose (or some other carbohydrate) to 

 the gelatin or agar. Gas bubbles will invariabl}^ appear if 

 the species is capable of producing gas at all. So far as mjr 

 observations have gone they show that all gas production is 

 linked to the presence of glucose or some other carbohydrate 

 in the culture medium. Before giving illustrations of this 

 process among different bacteria a few remarks on the mani- 

 pulation of the fermentation tube are in order. 



The fiuid used in all cases, with exceptions to be mentioned, 

 was peptone bouillon containing either glucose, lactose or 



