PREPAHATION OF BEEF- BROTH 57 



bonate, making the solution very faintly alkaline to litmus- 

 paper. The solution is again boiled for ten minutes, with 

 constant agitation. The reaction is again tested with 

 litmus-paper, and if still faintly alkaline, the solution is 

 filtered into a flask through a double-pleated filter-paper. 

 The filtered product, which should be absolutely clear and 

 bright,* is then run into flasks (which are plugged with 

 sterile cotton- wool and covered with tinfoil), and sterilised 

 on three successive days in the steamer for fifteen or twenty 

 minutes on each occasion. 



(2) Glycerine-broth. — To every 100 c.c. of beef-broth pre- 

 pared as above, 5 c.c. of glycerine is added, and shaken till 

 thoroughly mixed. The product is run into tubes, and 

 sterilized in the usual manner. Glycerine-broth is used 

 for the cultivation of the tubercle bacillus. 



(3) Grape-sugar-broth. — To each 100 c.c. of broth is 

 added 2 grammes of commercial glucose. When the 

 glucose is quite dissolved, the broth is sterilized as usual. 

 Grape-sugar-broth is used in the cultivation of anaerobic 

 bacteria. 



(4) Carbolated Broth. — This fluid is generally known as 

 Parietti's medium, and is used to restrain the growth of the 

 various putrefactive and ordinary water bacteria when it is 

 desired to isolate the Bacillus typhosus and Goli communis 

 from water. An aqueous solution is prepared, containing 

 5 per cent, of phenol and 4 per cent, of hydrochloric acid. 

 From 2 to 5 per cent, of this solution is added to ordinary 

 sterile nutrient broth. 



(5) Nutrient Gelatine. — This well-known and useful culture 

 medium, on which most organisms grow, giving rise to 



* If in spite of filtration the broth remains turbid, half the white of an 

 egg is added to the cooled broth, well mixed, then raised and maintained 

 at the boiling-point for ten minutes. The precipitated albumen is then 

 filtered off and the filtrate sterilised as above directed. 



