STUDY OF GASEOUS FERMENTATION 117 



EXERCISE 41. APPARATUS AND METHODS FOR THE 

 STUDY OF GASEOUS FERMENTATION 



Various forms of yeasts, bacteria and other micro- 

 organisms have the ability to ferment carbohydrate, nitrog- 

 enous, and other food substances with the liberation of gas. 



A. Smith's Fermentation Tube 



Theobald Smith (1893) introduced the use of a special 

 tube for studying fermentation and gas production, and 

 now Smith's fermentation tube is in general use in this 

 and other countries. 



Its value lies in the fact that it is a simple apparatus, 

 yet it allows not only of testing the relative fermentative 

 powers of different species of microorganisms or of different 

 strains of the same species, but of determining the gases 

 produced qualitatively and their relative proportions 

 quantitatively to some extent. 



Apparatus. Smith fermentation tubes; gasometer; 

 nutrient carbohydrate broth (or any desired solution); 

 platinum needles. 



Culture. Culture of the organism to be tested. 



Method. 1. The carbohydrate broth (or other liquid 

 medium) is placed in the fermentation tubes, filling the long 

 arm by carefully tilting. The bulb should be filled with 

 the liquid only to the extent that air will not enter the long 

 arm upon slightly tilting. The tube should not be filled 

 so full that the bulb will not contain all of the liquid in the 

 long arm. 



2. Sterilize. Carbohydrate broths are sterilized by the 

 intermittent method. 



3. Inoculate fermentation tubes of the desired medium 

 with the organism to be tested, using a loop or straight needle. 



4. Incubate at optimum temperature. 



5. Examine in twenty-four hours for gas production, 

 and mark the level of the liquid in the long arm of the 



