CULTURE MEDIA 39 



MISCELLANEOUS MEDDl 

 Medium 90 

 Litmus or Brom Cresol Purple Milk 



Litmus milk is one of the most important culture solutions. 

 Because of the great variety of organisms which grow in it, and 

 the decided changes which they produce, litmus milk is very 

 useful in the classification of bacteria. All organisms should be 

 inoculated into litmus milk and the changes after various 

 periods of time recorded. To secure the best results prepare 

 as follows : 



Fresh milk, immediately after milking, should be centrifuged 

 and this fat-free milk taken directly to the laboratory. Pipette 

 5- or 10- cubic centimeter portions of the fresh milk into pre- 

 viously sterilized test tubes, plug with cotton, and sterilize for 

 10 minutes in the autoclave at 8 to 10 -pounds^ pressure. Cool in 

 water and repeat sterilization 24 hours later. After the last 

 sterilization incubate the tubes for a week or more at 28 to 30°C. 

 and note if there are changes. Now add to each tube of the 

 bacteria free milk about 2 to 3 drops of a sterihzed saturated 

 solution of high-grade lime-free blue litmus (litmus 1 gram and 

 water, 15 cubic centimeters). Litmus milk should give a 

 lavender color, not too deep, which turns red in the presence of 

 acids and blue in the presence of alkalies. 



Brom cresol purple may be used in place of litmus. For 

 this purpose, prepare a stock solution as follows: 0.5 gm. of 

 brom-cresol purple should be ground in a mortar with 14 cubic 

 centimeters of .V/10 sodium hydroxide and made up to 100 cubic 

 centimeters with distilled water. Take 10 cubic centimeters of 

 this 0.5 per cent solution to 1,000 cubic centimeters of milk or 

 about 2 to 3 drops to 10 cubic centimeters of milk. 



Medium 91 

 Potato 



Select large potatoes, wash and scrub well with a stiff brush. 

 Peel and cut in wedge-shaped blocks about 4 to 6 centimeters 

 long and 1.5 centimeters wide. The size will depend upon the 



