CULTUEE METHODS 



26 



Exercise 37. Preparation of Dunham's Solution (for Indol Tests) 



Peptone . 

 Sodium chloride 

 Distilled water 



. 1.0 g. 

 . 0.5 g. 

 100.0 cc. 



r~\ 



Dissolve, place in test tubes, and sterilize as usual. Ten days 

 after inoculation, test for indol as 

 follows: add 1 cc. of 0.01 per cent 

 solution potassium nitrite and a few 

 drops of concentrated sulphuric acid. 

 Warm gently by putting tubes in 

 warm water. A pink color indicates 

 the presence of indol. The action of 

 an excess of sulphuric acid on peptone 

 causes a brown color in the solution. 



Exercise 38. Preparation of Phenol 

 Bouillon 



Add 1 g. of phenol (carbolic acid) 

 crystals to 1 liter of beef bouillon pre- 

 pared as directed in Exercise 8. This 

 medium is more frequently used for 

 the cultivation or isolation of B. coli. 

 A solid medium may be had by the 

 addition of gelatin or agar. 



Fig. 15. A fermentation tube 



Exercise 39. Preparation of Lactose Bile for Isolation of 

 Intestinal Bacteria 



1. Procure from the slaughterhouse an ox gall bladder. Empty 

 the bile into a graduated cylinder and add 1 per cent of lactose. 



2. Fill fermentation tubes and sterilize them in the Arnold 

 sterilizer. 



Exercise 40. Preparation of Neutral Red Broth 



Prepare beef bouillon in the regular way, adding 1 per cent 

 lactose, and to each 100 cc. of bouillon add 5 cc. of a 1 per cent 

 solution of neutral red (Griibler's Neutral Roth nach P. Ehrhch). 



Tube and sterilize in the Arnold sterilizer. 



