10 LABORATORY MANUAL OF MICROBIOLOGY 



Heat in steamer or double boiler for 1 hour, or until the upper 

 portion of the solution is clear. 



While hot filter through paper. 



Dissolve 12.5 grams of agar in 500 cubic centimeters of water. 

 Filter and mix the Nahrstoff-Heyden and agar solutions. 



It is not necessary to adjust the reaction of this medium. 



Medium 7 

 Soil-extract Agar 



Agar 12.5 gm. 



Glucose 1.0 gm. 



Dipotassium phosphate (K2HPO4) 0.5 gm. 



Soil extract (stock) ^ 100 . cc. 



Tap water 900.0 cc. 



1 Stock Solution of Soil Extract. — This is prepared by heating 1,000 grams 

 of garden soil with 1,000 cubic centimeters of tap water in the autoclave for 

 30 minutes. A small amount of calcium carbonate is added and the whole 

 is filtered through a double paper filter. The turbid filtrate should be poured 

 back on to the filter until it comes through clear. 



Dissolve the agar in 900 cubic centimeters of water by heating 

 in the steamer for 1 hour or longer. Add 100 cubic centimeters 

 of the stock soil-extract solution. 



Add the glucose just prior to tubing. 



The reaction should be pH 6.8. 



Medium 8 



Soil- EXTRACT Gelatin 2 



Gelatin 150.0 gm. 



Glucose 1.0 gm. 



Dipotassium phosphate (K2HPO4) 0.5 gm. 



Soil extract (stock) 100.0 cc. 



Tap water 900.0 cc. 



2 Conn, H. J., N. Y. Agr. Expt. Sta., Tech. Bull. 38, 1914. 



Dissolve the gelatin in the diluted soil-extract solution by 

 heating slowly in the steamer. 



Clarify the medium with egg albumen. 



Add 1 gram of glucose and adjust the reaction to pH 6.8. 



To prevent the spread of liquefying colonies add 5 grams of 

 sodium chloride (NaCl) per liter. 



