144 GENERAL MICROBIOLOGY 



16. What biochemical changes have occurred in the 

 decomposition? 



17. Compare the flora of fresh milk, 70 acid milk and 

 ten-day milk, both microscopically and from the plates. 

 Explain. 



18. State your results in detail and give any conclusions 

 to be drawn and any practical applications that may be 

 made. 



REFERENCES 



CONN: Practical Dairy Bacteriology, pp. 21-57, 81-85. 

 MARSHALL: Microbiology, pp. 298-299, 306-313, 321-326. 



EXERCISE 49. TO ISOLATE SPORE-FORMING BAC- 

 TERIA AND TO STUDY SPORE FORMATION 



Apparatus. Two tubes of sterile broth; small piece 

 of hay; three sterile Fetri dishes; clean test tube; three 

 tubes sterile agar for plates; three sterile agar slants; 

 carbol-fuchsin; acetic acid alcohol; aqueous-alcoholic 

 methylen blue; platinum needle and loop; ordinary for- 

 ceps. 



Culture. Hay. 



Method. 1. Place a piece of hay in the clean test 

 tube, plug the tube, and sterilize in the hot-air oven. 



2. Using sterile forceps, place the sterile hay " aseptic- 

 ally " in one tube of broth and an unsterilized piece in the 

 other. 



3. Incubate both at room temperature for forty-eight 

 hours. Do both tubes show growth? 



4. Heat in a water-bath at 80 C. for ten minutes the 

 tube which shows marked growth. What does this accom- 

 plish? 



5. Make three loop-dilution plates from the heated broth 

 tube. 



6. Place the plates at room temperature and examine 

 them daily for colony development. 



