SOIL BACTERIOLOGY 



8. Similar samples may be drawn after three or four 

 days and the amount of ammonia titrated. 



9. Tabulate the results. 



TABLE 9. Ammonification of Urea. 



Exercise 2 

 Isolation of Urea-fermenting Organisms 



1. Inoculate duplicate tubes of urea solutions as follows: 



(a) Medium 19 soil. 



(6) Medium 19 manure. 



(c) Medium 20 soil. 



(d) Medium 20 manure. 



A small inoculum is sufficient. In place of tubes (a) 

 and (6), cultures from the preceding exercise may be used. 



2. Two or three days after inoculation examine the test- 

 tube cultures for ammonia production (Nessler's reagent, 



P- i3S)- 



3. From one tube of each medium showing abundant 

 growth make transfers into tubes of sterile urea solution or 

 water blanks. A wide range of dilutions should be made. 



4. Pour plates from the different dilutions with the 

 same medium as in the tube culture plus gelatin (m. 23). 



