CULTURE MEDIA 41 



Some bacteria grow luxuriantly on a variety of media, others will only grow 

 on a few substances especially adjusted to their requirements. Hence, we have 

 a number of culture media, some used for the cultivation of bacteria in general 

 and others for the cultivation of one or several species. 



PREPARATION OF CULTURE MEDIA 



Litmus Milk. Fresh, sweet, cow's milk, which contains not more than 3 

 per cent, fat: 



1. Add aqueous sol. of litmus, sufficient to give a faint blue tint. 



2. Sterilize in Arnold steam sterilizer, i hour each day for 3 consecutive days. 

 Plain Bouillon (Meat extract broth) . 



1. Beef extract (Liebig's), 2 Gm. 



2. Beef peptone (Witte's), 10 Gm. 



3. Sodium chloride, 5 Gm. 



4. Water, 1000 cc. 



Make a paste of the peptone; then dissolve it in water, add the salt and beef 

 extract. Boil and stir for % hour, make up for evaporation by the addition of 

 water, again bring to boiling point. Test for alkalinity or acidity and properly 

 adjust the reaction. Filter while hot and again when cool. Sterilize in auto- 

 clave. 



Plain Bouillon (Meat infusion broth). 



1. Minced lean meat (beef or veal), 500 Gm. 



2. Water, 1000 cc. 



Place in ice box in shallow dish for 24 hours. Skim off fat, filter through 

 linen and express juice contained in the meat. 



Boil for 2 hours, filter through linen and boil again for i hour. Add water 

 to make up for loss by evaporation, add peptone 10 Gm. and sodium chloride 

 5 Gm., boil for J^ hour, make up for evaporation, adjust reaction, filter while 

 hot and again when cool. Sterilize in autoclave. 



Sugar-free Bouillon. Make meat infusion broth, introduce bacillus coli 

 and incubate for 24 hours at 37C., boil for J^ hour, filter while hot and again 

 when cool. Adjust reaction and sterilize. 



Sugar Bouillon. Various sugars are added to plain bouillon or stigar-free 

 bouillon to study fermentation. Glucose, lactose and saccharose are most 

 commonly used. J^ to 2 Gm. to 100 cc., J^ to 2 per cent. 



Bouillon containing sugar is often tinted a faint blue by adding litmus; this 

 is to act as an indicator of acid production. 



Culture media containing sugars are sterilized in the Arnold steam sterilizer 

 (iooC.) 20 minutes each day for 3 days. 



Glycerin Bouillon. 



1. Plain bouillon, 100 cc. 



2. Double distilled glycerin, 6 cc. 

 Sterilize in autoclave. 



