280 GENERAL MICROBIOLOGY 



9. At the end of another twenty-four hours repeat the 

 titrations and platings with all flasks, using the following 

 dilutions : 



Flask A, 1 : 10,000 and 1 : 1,000,000. 



Flasks B and C, 1 : 1,000,000 and 1 : 100,000,000. 



10. At the end of five days determine and record the 

 acidity of the milk in all flasks. Plate from flask A only, 

 using dilutions of 1 : 1,000,000 and 1 : 100,000,000. 



11. All plates should be held at 21 C. for a period of 

 five days before counting. 



12. Compare the relative kinds and numbers of colonies 

 in plates from the three flasks. Note also the time of curd- 

 ing and the nature of the curd formed in each case. 



13. Compile the results of the investigation in tabulated 

 form. Plot bacterial count and acidity curves. 



14. From the results obtained, what conclusions would 

 you draw as to the influence of cooling upon the keeping 

 quality of milk? 



How does the age and original quality of the milk effect 

 its keeping qualities when subjected to different temperature 

 conditions? 



How dpes cooling milk and keeping it cool compare with 

 merely cooling and then allowing the milk to acquire the 

 temperature of the room? What is the explanation of the 

 action occurring? 



What is the purpose of cooling the milk as soon as it 

 comes from the cow? What different methods are used? 

 What are some of the disadvantages of the different methods 

 used for cooling? 



What bacterial action takes place in the refrigerator 

 milk? Is the germicidal action of milk sufficiently important 

 to recommend a change in the general practice of cooling 

 milk? 



15. Give your results in detail and point out any 

 practical applications or conclusions. 



