vni EXAMINATION OF SOIL 115 



at C, and place the flask with the roll tubes in the cool 

 incubator for several days. 



(12) Then examine the tubes for colonies, and make sub- 

 cultures in grape-sugar gelatine (stab cultures), and place 

 them in a wide-necked bottle, and proceed as just described. 



This method is fairly convenient as a means of separ- 

 ating anaerobic organisms. 



Examination of Soil 

 A. SURFACE SOIL. 



(1) Scrape a little earth from the surface of the ground 

 with a sterile knife or spoon, and collect it in a sterile 

 beaker. 



(2) Introduce small quantities of it into a number of 

 liquid gelatine tubes with a platinum loop, and gently 

 shake the tubes, so as to distribute the particles of earth as 

 uniformly as possible. 



(3) Prepare dilutions in the usual manner. 



(4) Make roll tubes as previously described, and place 

 some of these in the cool incubator. 



Examine the tubes from day to day, and prepare sub- 

 cultures from the colonies as they appear. 



(5) Place the remaining roll tubes in a large wide-necked 

 bottle as described in the previous section (vide Fig. 10) ; 

 and having exhausted the flask, place it in the cool in- 

 cubator. 



Examine the tubes from day to day, and prepare sub- 

 cultures in grape-sugar gelatine (deep stab cultures). 



