124 BACTERIOLOGY. 



solution to ueutralize it, lactose is added in the propor- 

 tion of 2 or 3 per cent. ; it is then decanted into test- 

 tubes and sterilized in the usual way. When ster- 

 ilization is complete enough sterilized litmus tincture 

 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. 



Lqffler's blood-serum mixture. LofEler's blood-serum 

 mixture consists of one part of neutral meat-infusion 

 bouillon, containing 1 per cent, of gi'ape-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.) 



Guarniari's agar-gelatin : 



Meat-infusion . 950 c.c. 



Sodium chloride . 5 grammes. 



Peptone . 25-30 " 



Gelatin ... , . 40-60 " 



Agar-agar 3-4 " 



Water . 50 c.c. 



The special point in the preparation of tliis medium 

 is its reaction, which should be exactly neutral. 



The full list of special media is too extensive to be 

 given in a book of this size. For their description the 



