SPECIAL MEDIA. 107 



nipulation. It is better not to add the litmus tincture 

 before sterilizing the tubes, as its color-characteristics 

 are in some way altered by its contact with organic 

 matters under the influence of heat. 



When ready it may be used as ordinary agar-agar or 

 gelatin, either for plates or slant-cultures. 



Loeffler's blood-serum mixture. Loeffler'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.) 



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 point in the preparation of this medium is its 

 reaction, which should be exactly neutral. 



The full list of special media is too great to be given 

 in a work of this size. For their description the reader 

 is referred to the current literature on the subject. 

 Those that have been given above will suffice for ob- 

 taining a clear understanding of the principles of the 

 work. 



NOTE. The term "meat-infusion " always implies a 

 watery extract of meat made by mixing 500 grammes 



