NUTRIENT MEDIA 53 



bulk is calculated and added ; the reaction of the medium 

 will then be exactly neutral. The medium is then rendered 

 faintly alkaline by the addition of 1 c.c. of normal soditim 

 carbonate solution to each 100 c.c. of nutrient medium. 

 This degree of alkalinity, we find, gives the best results in 

 practice. 



(2) Glycerine-brotL — 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 

 sterilised in the usual manner. Glycerine-broth is used 

 for the cultivation of the tubercle bacillus. 



(3) Grape-sug^ar-broth. — To each 100 c.c. of broth is 

 added 2 grammes of commercial glucose. When the 

 glucose is quite dissolved, the broth is sterilised 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 Coli communis 

 from water. An aqueous solution is prepared, containing 

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

 Prom 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 

 very characteristic growths, cannot be used for temperatures 

 above 20° C, as its melting-point is about 22° C, or a little 

 higher. The nutrient gelatine prepared according to the 

 formula of Koch and Loffler is the one most in use, and is 

 made as follows: One pound of beef-steak is minced, as 

 directed under the preparation of beef-broth, and digested 

 with 1,000 c.c. of water, which is then slowly raised, with 

 stirring, to the boiling-point. The infusion is then strained 



