252 GENERAL MICROBIOLOGY 



any nitrites or ammonia have developed. To what are 

 the gas bubbles due? 



The crystals deposited in Giltay's solution are magnesium 

 phosphate. 



4. Using sterile pipettes, test 1 c.c. portions of each 

 after forty-eight hours, seven days, etc., for nitrates with 

 phenolsulphonic acid. 



5. From two tubes showing abundant gas formation, 

 make nitrate agar plates, using a wide range of dilutions 

 that one or two plates may show well-isolated colonies. 

 Incubate at 37 C. 



6. From various colonies appearing on the plates, make 

 stab cultures in nitrate agar. Incubate these at 37 C. 



Save one showing the most abundant gas formation under 

 these conditions, for further study. 



7. Inoculate a nitrate bouillon fermentation tube with 

 the pure culture just isolated, also add some of the crude 

 material to a fermentation tube. 



8. Duplicate with a nitrate bouillon fermentation tube 

 containing sugar. 



9. Determine the amount and nature of the gas formed 

 in each tube and compare results. (Determine by elimi- 

 nation; test for CO2 and H2.) 



What influence does dextrose have upon the rate and 

 amount of gas formation? 



10. Inoculate in duplicate, tubes of peptone solution 

 with the pure culture. Record the growth and gas forma- 

 tion, if any, qualitatively. 



11. To an old culture (not necessarily pure) in which the 

 nitrates have disappeared, add 1 c.c. of a sterile 1% solu- 

 tion of KNOs. Does gas formation re-occur? 



12. Continue to add a small amount of KNOs as rapidly 

 as the culture ceases to give a reaction for nitrates (an 

 indication that the latter have been used up.) Note how 

 much KNOs your culture can reduce. 



13. Theoretically, what would be the difference in 



