DENITRIFICATION IN SOLUTION 251 



Their respective functions? What interrelationships exist 

 between these organisms? 



Where are nitrifying organisms found in nature? What 

 is their significance? 



W^hat conditions in soil are necessary for their pro- 

 liferation? What methods does the agriculturist use which 

 serves to conserve these organisms? 



REFERENCES 



LOHNIS: Laboratory Methods in Agricultural Bacteriology, pp. 



96, 97, 106, 109, 110. 

 LIPMAN and BROWN: Laboratory Guide in Soil Bacteriology, pp. 



25-34. 

 MARSHALL: Microbiology, pp. 259-263. 



EXERCISE 7. TO ILLUSTRATE DENITRIFICATION IN 

 SOLUTION 



Apparatus. Eight tubes of sterile Giltay's solution; 

 eight tubes of nitrate broth; eight to ten tubes of Giltay's 

 agar; eight to ten tubes of nitrate agar; eight fermenta- 

 tion tubes of nitrate bouillon, four with and four .without 

 sugar (use 1% dextrose); peptone solution in tubes; sterile 

 1% solution of KNOs; nitrate test solution; Nessler's 

 solution, test for NHs; a-naphthylamin and sulphanilic acid 

 (nitrite test solutions); sterile 1 c.c. pipettes; sterile Petri 

 dishes; sterile dilution flasks. 



Cultures. Soil (record type used); straw from manure 

 pile; horse manure. 



Method. 1. Inoculate test tubes of each solution in 

 series as follows: 



1 and 2 



3 and 4 0.1 gm. soil. 



5 and 6 0.1 gm. straw; 



7 and 8 0.1 gm. horse manure. 



2. Incubate these at 37 C. for forty-eight hours. 



3. Note any changes occurring. Determine whether 



