CHAPTER V. 



Preparation of media Bouillon, gelatin, agar-agar, potato, blood-serum, etc. 



As has been stated, the fundamental part of our cul- 

 ture 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 his original 

 formula is still retained. It is as follows : Five hundred 

 grammes of finely-chopped lean beef, free from fat and 

 tendons, is to be soaked in one litre of water for twenty- 

 four hours. During this time it is to remain in the 

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

 It is then to be strained through a coarse towel and 

 pressed until a litre of fluid is obtained. To this is to be 

 added ten grammes (1 per cent.) of dried peptone and 

 five grammes (0.5 per cent.) of common salt (ISaCl). It 

 is then to be rendered exactly neutral or very slightly 

 alkaline, with a few drops of saturated sodium carbon- 

 ate solution. The flask containing the mixture is then 

 to be placed either in the steam sterilizer or in a water- 

 bath, or over a free flame, and kept at a boiling-point 

 until all the albumin is coagulated, and the fluid portion 

 is of a clear, pale, straw-color. It is then filtered 

 through a folded paper filter, and sterilized in the steam 

 sterilizer by the fractional method. Certain of the 

 modifications of this method are of sufficient value 

 to justify mention. Most important is the neutraliza- 



