14 LABORATORY MANUAL OF MICROBIOLOGY 



Dissolve the salts, peptone and agar by steaming for H to 1 

 hour, adjust the reaction to pH 3.8 to 4.0 with N/1 H2SO4 

 (about 5 to 7 cubic centimeters of N/1 per liter) and then add 

 the glucose. Filter through cotton, using a suction flask. 

 Because of the acid reaction steriUze in the autoclave at 110°C. 

 (7 to 8 pounds pressure) not more than 10 minutes. Avoid 

 excessive heat. 



The medium may be prepared without addition of acid, 

 filtered, then placed in 100-cubic centimeter portions, in Erlen- 

 meyer flasks and sterihzed. Whenever needed for use, the agar 

 is melted by placing flasks in boiling water. One cubic centimeter 

 of N/2 H2SO4 is then added to each flask giving the desired 

 reaction. 



Medium 19 



Potato-glucose Agar 



Agar 30.0 gm. 



Potato 200.0 gm. 



Glucose 20.0 gm. 



Tap water 1,000.0 cc. 



Peel and shce 200 grams of potatoes. Cook in 1,000 cubic 

 centimeters water for 1 hour in the steamer. Strain or decant 

 the clear Hquid and restore it to the original volume. Add 20 

 grams glucose and 30 grams agar. Heat in steamer until the 

 agar is dissolved. Filter through cotton filter. 



Medium 20 



ASPARAGIN-STARCH AgAR^ 



(Brown, modified for color formation) 



Agar 15.00 gm. 



Potato starch 10.00 gm. 



Asparagin . 20 gm. 



Potassium phosphate, ortho (K3PO4) 1-25 gm. 



Magnesium sulphate (MgS04-7H20) . 75 gm. 



Water 1,000.00 cc. 



1 Brown, W., Ann. BoL, 39: 405, 1925. 



