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 



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

 ize in the arnold. 



MacConkey's bile-salt broth 



Sodium taurocholate 0.5 per cent 



Pepton 2 per cent 



Dextrose 0.5 per cent 



Dissolve in beef broth by boiling, filter, and add 

 litmus solution. Sterilize in the arnold. 

 Aesculin bile-salt agar 



Agar 15 g rams 



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 boiling 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. 



