62 APPLIED BACTERIOLOGY 



(9) Glycerine Agar. — This is prepared by the addition of 

 5 per cent, of pure glycerine to the nutrient agar prepared 

 as above. This addition is particularly valuable, as it 

 prevents the drying up of the medium, and is useful for 

 growing the tubercle bacillus. 



(10) Grape-sugar Agar. — The addition of 2 per cent, of 

 glucose to nutrient agar is useful for the cultivation of 

 anaerobic bacteria. The tubes for this purpose are filled 

 two-thirds full. 



(H) Urine Gelatine and Agar.— Fresh urine thickened 

 with 10 per cent, of gelatine, or 2 per cent, of agar, with 

 the addition of 1 per cent, of peptone and ^ per cent, of 

 sodium chloride, is rendered feebly alkaline and filtered. 

 The details of the method of preparation are the same as 

 those already described for nutrient agar and gelatine. 

 These two media are largely used in Germany, and are 

 said to yield equally satisfactory results to those prepared 

 from broth. 



(12) Peptone Solution. — Ten grammes of peptone and five 

 grammes of sodium chloride are dissolved in 1,000 c.c. of 

 distilled water ; the solution is then well boiled, and neutra- 

 lised carefully in the usual manner. The solution is again 

 boiled and filtered. The solution is then run into tubes, 

 and steamed for fifteen minutes on three successive days. 

 These tubes are used in the diagnosis for cholera. 



(13) Milk-tubes. — ' Separated ' milk is carefully neutra- 

 lised with sodium bicarbonate and filled into tubes, and 

 sterilised as usual. These tubes are useful for the differ- 

 entiation between typhoid and cholera. 



Reaction of Media. — Some bacteria grow readily in a 

 medium having an acid reaction, while the faintest trace of 

 acid will prevent the growth of others. As a rule, the 

 pathogenic species require a neutral or slightly alkaline 

 medium. 



