MUTUAL RELATIONSHIP OF MICROORGANISMS 215 



with Bad. ladis acidi, flask B with Bad. ladis acidi and 

 Oospora ladis, and flask C with Oospora ladis alone. 



3. Make ten titrations, titrating every two or three days 

 (not oftener) and record the titrations. Tabulate the 

 data. 



4. Plot curves. How do you explain the direction these 

 curves take? 



5. At the end of the titrations, make loop transfers 

 from each flask into litmus milk tubes and watch these 

 carefully in the next twenty-four to forty-eight hours. 

 Record the results. 



6. Does the action in the flasks appear to be symbiotic? 

 If so, how is it shown? 



Is this symbiosis desirable or not? Explain. 

 What other well-known examples of symbiosis occur in 

 nature? Give a reason for your statement. 



7. Give all data and results in full. Draw any conclu- 

 sions that follow and point out any practical operations. 



REFERENCES 



MARSHALL: Microbiology, pp. 181-182, 273-282, 323. 



NORTHRUP: The Influence of Certain Acid-destroying Yeasts upon 



Lactic Bacteria. Tech. Bui. No. 15, Mich. Expt. Sta., pp. 8-16, 



32-34. 



EXERCISE 32. TO ILLUSTRATE ONE OF THE PHASES 

 OF MUTUAL RELATIONSHIP OF MICROORGANISMS 



Apparatus. Sterile 5 c.c. pipette; 3 sterile 200 c.c. 

 Erlenmeyer flasks; 450 c.c. sweet cider (that from pas- 

 teurization experiment may be used). 



Cultures. Sacch. ellipsoideus, Bad. aceti. 



Method. 1. Place 150 c.c. of sweet cider in each flask. 



2. Determine and record the reaction of the cider, 

 then heat the flasks thirty minutes in the steam. 



3. Cool the flasks and inoculate flask A with Sacch. 

 ellipsoideus. 



