BACTERIOLOGICAL TECHNIC 33 



phthalein, the solution is then filtered and sterilized 

 in the arnold for three successive days. 



Dextrose yeast water. — ^Dissolve 10 to 15 per cent 

 dextrose in yeast water without adjusting the reaction. 



EXERCISE 12. PREPARATION OF. MEDIA FOR THE DIF- 

 FERENTIATION OF B. coli AND B. typhosus 

 MacConkey's bile-salt agar — 



Nutrient agar 100 c.c. 



Sodium taurocholate • 0.5 per cent 



Pepton 2 per cent 



BoU and filter, add 2 per cent lactose, tube and steril- 

 ize in the arnold. 



MacConkey's bile-salt broth — 



Sodium taurocholate o . j per cent 



Pepton 2 per cent 



Dextrose o. 5 per cent 



Dissolve in beef broth by boiling, filter, and add 

 litmus solution. Sterilize in the arnold. 

 Aesculin bile-salt agar — 



Agar IS grams 



Commercial bile-salt 2.5 grams 



Pepton (Witte) 10 grams 



Distilled water 1,000 c.c. 



Boil until dissolved and neutralize with n.NaOH. 

 Cool to 60° C, add .the whites of two eggs or a solu- 

 tion of egg albumin, bring to boiUng point, and filter 

 when the albumin has coagulated. Neutralize again, 

 if necessary, and add to the hot filtrate i gram aesculin 

 and I gram iron citrate in scales. The final reaction 

 should be 0.6 per cent acid. 



