474 BACTERIOLOGICAL ANALYSES 



Tubes of glucose formate agar. 

 Water-bath regulated at 42 C. 

 Bunsen burner. 

 Grease pencil. 



Sterile mortar and pestle (agate) . 



Sterile wide-mouthed Erlenmeyer flask (500 c.c. capacity). 

 Sterile metal funnel with short wide bore delivery tube to 

 just fit mouth of flask. 



Solid rubber stopper to fit the flask (sterilised by boiling) . 



Pair of scales. 



Counterpoise (Fig. 107). 



Sterile metal (nickel) spoon or spatula. 



Fractional steriliser (Fig. 140). 



METHOD. 



1. Arrange four sterile capsules numbered I, II, III, 

 and IV; pipette 9 c.c. sterile bouillon into the first 

 capsule, and 9.9 c.c. into each of the remaining three. 



2. Pipette 100 c.c. sterile bouillon into the Erlen- 

 meyer flask. 



3. Remove the cotton -wool plug from the flask and 

 replace it by the sterile funnel. 



4. Place flask and funnel on one pan of the scales, 

 and counterpoise accurately. 



5. Empty the sample of soil into the mortar and 

 triturate thoroughly. 



6. By means of the sterile spatula add 10 grammes 

 of the earth sample to the bouillon in the flask. 



The final results will be more reliable if steps 2, 3, 4, 

 and 5 are performed under a hood to protect from 

 falling dust, etc. 



7. Remove the funnel from the mouth of the flask; 

 replace it by the rubber stopper and shake vigourously ; 

 then allow the solid particles to settle for about thirty 

 minutes. One cubic centimetre of the turbid" broth 

 contains the washings from o.i gramme of soil. 



8. Pipette off i c.c. of the supernatant bouillon, 

 termed the "soil water," and add it to the contents 

 of capsule I ; mix thoroughly. 



9. Remove o.i c.c. of the infected bouillon from 

 capsule I and add it to capsule II, and mix. 



