218 GENERAL MICROBIOLOGY 



A for obtaining the initial number of Bad. lactis acidi 

 introduced per c.c. 



4. Continue as follows: 



Flask A; 



2d day, titrate and use dilutions 1-10,000, 



1-100,000 and 1-1,000,000. 

 3d day, titrate and use dilutions 1-1,000,000, 



1-10,000,000 and 1-100,000,000. 

 6th day, titrate and use dilutions 1-100,000, 



1-1,000,000 and 1-10,000,000. 

 7th day, titrate and use dilutions 1-1,000, 



1-10,000 and 1-100,000. 



N. B. Shake the flask of milk well each time before titrat- 

 ing and making dilutions. 



5. Titrate and plate every third day thereafter, until the 

 acidity remains constant. 



6. In flask B from day to day note in millimeters the 

 extent of the re-oxidation of the azolitmin. 



7. Flask B. Without disturbing the milk any more than 

 necessary, make a loop transfer every day or so for 10 to 

 14 days from this flask into a tube of sterile litmus milk. 



What occurs in each case? In what respects does 

 flask B check up with flask A? Give explanations for sim- 

 ilarity or dissimilarity of actions occurring. 



8. Milk contains on an average about 4.5% lactose. 

 Has this sugar been fermented entirely to lactic acid? 

 Explain what really occurs. 



9. What titre would milk containing 5% lactose have 

 if this sugar were entirely changed to lactic acid? 



Does any lactic-acid-producing organism approximate 

 this reaction (in milk) at the height of its activity? 



10. Give reasons for what occurs in each flask. What 

 practical applications may this experiment have? 



11. Tabulate your results and plot number and acidity 

 curves. Explain these curves. 



