194 DIFGO MANUAL 



Ulrich Milk, when first taken from the autoclave after sterilization, is nearly 

 white in color but quickly develops a bluish-gray top layer with a pink under 

 portion. As the methylene blue oxidizes the blue color extends progressively 

 downward until the entire medium is uniformly bluish-gray. In contrast. Litmus 

 Milk takes on a pink coloration. 



When inoculated with lactic acid producing organisms Ulrich Milk first 

 changes to a pale pink in the subsurface areas, the upper layer remaining blue. 

 The depth of the top layer will depend on the rate of reduction of the methylene 

 blue by the growing organism against air oxidation. As more acid is produced 

 the blue top layer changes to a pale yellow-green and the pink portion fades to 

 white and then becomes a pale yellow-orange. If the medium does not become 

 coagulated, or if acid is produced slowly, 60 per cent of the tube may be yellow- 

 ish-green in color. If the medium is coagulated the greenish zone is limited to a 

 narrow band or collar at the top because of the decreased oxidation. In Litmus 

 Milk, as acid is produced, the pink color develops, and as the litmus is reduced, 

 especially in the lower portion of the tube, the medium becomes white. 



Proteolytic organisms, or those producing alkali, do not generally coagulate 

 milk. In Ulrich Milk they change the lower portion of the tube from blue to 

 white and then to pink. If peptonization occurs the medium becomes transparent 

 and reddish-purple in color. 



To rehydrate the medium, dissolve 100 grams of Bacto-Ulrich Milk in 1000 

 ml. distilled water. Distribute into tubes or flasks as desired and sterilize for 15 

 minutes at 15 pounds pressure (121°C.). Overheating during sterilization results 

 in the carmelization of the milk sugar. This is to be avoided since this resulting 

 discoloration may give an atypical appearance to the sterile medium which may 

 be further reflected in the appearance of growing cultures. The final reaction of 

 the medium will be pH 6.5. 



One pound of Bacto-Ulrich Milk will make 4.5 liters of medium. 



1 Science, 99:352:1944. s Munsell Color Company, Inc., Bedtimore, 



3 Color Standards and Color Nomenclature, 1912. Maryland. 



ADDITIONAL MEDIA 



The media listed below have been rather extensively employed in the past. 

 Recently other media have been developd which are considered superior and 

 serve the purpose more adequately than the older media. For the present we will 

 continue to carry these media in stock for those laboratories where they have 

 been in routine use, or where it is desired to continue them for comparative 

 purposes. 



PRESENT RECOMMENDATIONS 



Bacto-B.T.B. Lactose Agar Bacto-Mannitol Salt Agar, page 150 



Bacto-Crystal Violet Agar Bacto-Staphylococcus Medium No. 110, page 151 



Bacto-Stone Gelatin Agar Bacto-Chapman Stone Medium, page 153 



Bacto-Purple Milk Bacto-Litmus Milk, page 192 



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