CHAPTER V. 



Preparation of media Bouillon, gelatin, agar-agar, potato, blood 

 serum, blood-serum from small animals, milk, litmus-whey 

 milk, Durham's peptone solution, lactose litmus-agar, Loeffler's 

 blood-serum mixture, the serum-water media of Hiss, Guarni- 

 ari's gelatin-agar mixture. 



As has been stated, the fundamental constituent of 

 culture-media is beef-tea, or bouillon. 



BOUILLON. The directions of Koch for the prepara- 

 tion of this medium have undergone many modifications 

 to meet special cases; but for general use the formula 

 now employed is as follows : 500 grammes of finely 

 chopped lean beef, free from fat and tendons, are to be 

 soaked in one litre of water for twenty-four hours, dur- 

 ing 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 grammes (1.0 per cent.) of 

 dried peptone and 5 grammes (0.5 per cent.) of common 

 salt (NaCl). It is then to be rendered exactly neutral 

 or very slightly 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 coagulated and the fluid 

 portion is of a clear, Dale straw color. It is then filtered 



