THE EFFECT OF AERATION OF SOILS 



245 



EXERCISE 3. TO ILLUSTRATE THE EFFECT OF AERA- 

 TION OF SOILS ON THE ACTIVITIES OF THE MICRO- 

 ORGANISMS CONTAINED THEREIN 



Apparatus. Coarse, medium, and fine sand; magnesium 

 oxide; dilute HC1; N/10 NH 4 OH; N/10 HC1; indicator; 

 sterile 1 c.c. pipette; ten sterile 250 c.c. Erlenmeyer flasks; 

 condenser; sterile 1% peptone solution. 



Culture. B. mycoides, broth culture. 



Method. 1. Prepare the sand for use by first heating 

 it with dilute HC1; then wash it several times, first with 

 tap water then with distilled water and dry at 110 C. 



2. Place 50 gms. of coarse sand in each of three flasks; 

 do the same with the medium and the fine sand. 



3. Sterilize the flasks in the autoclav at 120 C. for 

 thirty minutes. 



4. Place 50 c.c. of the 1% peptone solution in the remain- 

 ing flask. 



5. Add sufficient peptone solution to the other flasks 

 to make 10%, 20% and 30% moisture content according 

 to the following table : 



6. Inoculate each flask with 1 c.c. from a broth culture 

 of B. mycoides and shake to distribute the organisms evenly. 



