192 GENERAL MICROBIOLOGY 



REFERENCES 



BAYLISS: Nature of Enzymic Action, pp. 140-141. 



EULER-POPE: General Chemistry of the Enzymes, pp. 65, 67-68. 



VERNON: Intracellular Enzymes, pp. 127-132. 



LOHNIS, F.: Laboratory Methods in Agricultural Bacteriology, pp, 



66-67, 79. 

 MARSHALL; Microbiology, pp. 135, 142-143. 



EXERCISE 17. TO DEMONSTRATE THE OXIDIZING 

 ENZYME OF VINEGAR BACTERIA 



Apparatus. 200 c.c. fermented cider (or other fruit 

 juice); sterile 375 c.c. Erlenmeyer flask; sterile 10 c.c. 

 pipette; water bath; specific gravity bottle. 



Culture. Bad. aceti. 



Method. 1. Place the cider in a sterile flask and heat 

 in a water bath at 60 C. for one hour. Cool quickly. What 

 is this process called? 



2. Determine the specific gravity of the fermented 

 cider. 



3. Inoculate with a pure culture of Bact. aceti and titrate 

 every three days until the titre is constant. 



4. Plot the curve showing and explain the direction 

 which the curve takes. What is taking place? Enzyme? 

 Chemical equation? 



5. Determine the specific gravity of the solution at the 

 last titration. ..How does this compare with specific gravity 

 of cider vinegar of legal standard? What is the legal stand- 

 ard for vinegar in this state? Can you explain why all 

 vinegar does not come up to the legal standard? 



6. Is it practicable to use pure cultures for preparing 

 vinegar? How do various species of vinegar bacteria differ 

 from one another? 



Under what conditions will acetic fermentation set in 

 " spontaneously? " 



What raw materials will give rise to a vinegar by a 

 normal acetic fermentation? 



