136 BACTERIOLOGY. 



should be added to each tube to give a decided, though 

 not very intense, blue color. This must be done care- 

 fully, to avoid contamination of the tubes during ma- 

 nipulation. It is better not to add the litmus tincture 

 before sterilizing the tubes, as its color-characteristics 

 are altered by contact with organic matters under the 

 influence of heat. This medium is used for both test- 

 tube and plate cultivation, just as is ordinary agar-agar 

 and gelatin. 



Loffler's blood-serum mixture. Loffler's blood-serum 

 mixture consists of one part of neutral meat-infusion 

 bouillon, containing 1 per cent, of grape-sugar, and 

 three parts of blood-serum. This mixture is placed in 

 test-tubes, sterilized, and solidified in exactly the way 

 given for blood-serum. It requires for its solidification 

 a somewhat higher temperature and a longer exposure 

 to this temperature than does blood-serum to which no 

 bouillon has been added. (See also the Councilman- 

 Mallory method.) 



The Serum-water Media of Hiss. A medium which 

 has been found very serviceable in the differentiation 

 between closely related bacteria is prepared by mixing 

 one part of blood-serum (either horse or bovine) and 

 three parts of distilled water. This is neutralized, and 

 heated in a water-bath or an Arnold steam sterilizer 

 until it becomes opalescent. A 5 per cent, aqueous 

 solution of litmus is then added in the proportion of 1 

 per cent. Any one of the carbohydrates, as dextrose, 

 lactose, saccharose, levulose, mannite, etc., is then added 

 in the proportion of 1 per cent. The finished medium 

 is then placed in test-tubes. The medium must be ster- 

 ilized in an Arnold steam sterilizer, and it is advisable 

 to allow the sterilizer to remain uncovered during the 



