CHAPTER V. 



Preparation of Media — Bouillon, Gelatin, Agar-agar, Potato, Blood-serum, 

 Blood-serum from Small Animals, Milk, Litmus-whey Milk, Dur- 

 ham's Peptone Solution, Lactose Litmus-agar, LofHer's Blood-serum 

 Mixture, the Serum-water Media of Hiss, Guarniari's Gelatin-agar 

 Mixture. 



As has been stated, the fundamental constituent of cul- 

 ture-media is beef-tea, or bouillon. 



BOUILLON. 



The directions of Koch for the preparation of this medium 

 have undergone many modifications to mieet special cases; 

 but for general use the formula now employed is as follows: 

 500 grams of finely chopped lean beef, free from fat and 

 tendons, are to be soaked in 1 liter of water for twenty- 

 four hours, during which time the mixture is to remain in 

 an ice-chest or to be otherwise kept at a low temperature. 

 At the end of twenty-four hours it is to be strained through 

 a coarse towel and pressed until a litre of fluid is obtained. 

 To this are to be added 10 grams (1 per cent.) of dried 

 peptone and 5 grams (0.5 per cent.) of common salt (NaCl). 

 It is then to be rendered exactly neutral or very sHghtly 

 alkaline to litmus paper with a few drops of a 4 per cent, 

 sodium hydroxide solution. The mixture is then placed in 

 an agate ware or porcelain-lined saucepan over a free flame, 

 and kept at the boiling-point until all the albumin is coagu- 

 lated and the fluid portion is of a clear, pale straw color. 

 (108) 



