AMMONIFICATION OF VARIOUS SUBSTANCES 39 



Exercise 5 

 Isolation of Ammonifying Organisms 



1 . As soon as the cultures of the preceding exercise begin 

 to show a vigorous ammonia production, make loop trans- 

 fers to tubes of sterile gelatin solution or sterile water. 



2. Repeat the dilution four times. 



3. Pour gelatin (m. 2) or agar (m. 3) plates from dilu- 

 tions i : 10,000 and i : 1,000,000, using i-c.c. portions 

 for each plate. 



4. After colonies have developed, pick several pure 

 cultures. These should be transferred to gelatin solution 

 and their ammonifying power studied. For this purpose 

 use Nessler's reagent. 



5. Select two of the organisms that produce the largest 

 amount of ammonia. These should be kept for a later 

 study. 



6. Prepare stained mounts of these organisms. 



Exercise 6 

 Ammomfication of Various Substances 



1. Prepare twelve 5o-gram portions of field-soil in clean, 

 dry tumblers. The soil should be mixed thoroughly be- 

 fore samples are drawn. 



2. Treat the soils as follows: 



(a) i, 2, 3, and 4, add i per cent, of casein. 



(&) 5> 6 > 7> an( l 8 > a( ld i per cent, of blood-meal. 



(c) 9, 10, n, and 12, add i per cent, of dried clover hay. 



3. Add these substances in the powdered form and mix 

 thoroughly. 



