42 LABORATORY MANUAL OF MICROBIOLOGY 



Medium 98 

 Peptone-beef Extract Gelatin Agar^ 



(a) Sodium chloride (NaCl) 5.0 gm. 



Monopotassium phosphate (KH2PO4) 0.5 gm. 



Dipotassium phosphate (K2HPO4) 1.5 gm. 



Water ■ 100.0 ec. 



(6) Gelatin 4.0 gm. 



Glucose . 05 gm. 



Peptone 0.1 gm. 



Beef infusion 5.0 cc. 



Water 400 . cc. 



1 Frazier, W. C., J. Inf. Dis., 39: 302, 1926. 



Pour (a) and (h) together, heat in flowing steam and mix with 

 500 cubic centimeters of a 3 per cent agar (washed) solution. 



Adjust pH to 7.0. 



Pour duplicate plates and inoculate in the center. After 

 48 hours or longer at 30°C. make tests. 



Flood one plate with 1 per cent tannic acid and the duplicate 

 with acid HgCl2 solution.^ 



^HgCU 15 grams, HCl (Cone) 20 cubic centimeters, and 100 cubic 

 centimeters of water. 



If the gelatin has been changed, a clear zone will appear about 

 the giant colony in the plate to which HgCl2 has been added. 

 This requires 15 to 30 minutes. 



The tannic acid plate will show the amount of decomposition 

 of the gelatin. 



Medium 99 

 Casein Hydrolysis on Milk Agar 



(a) Agar 15.0 gm. 



Water 500.0 cc. 



(6) Milk 500.0 cc. 



Tube separately in portions for plating. Sterihze. Cool to 

 45°C. and pour plates using one tube of each per plate. 



Streak the culture to be tested on the surface of the milk agar. 



After incubation examine the plates for clearing along line of 

 growth. Flood plates with dilute acid (HCl 1:10). If clearing 

 remains, it denotes true hydrolysis of casein. If not, it is weak 

 acid clearing. 



