EXAMINATION OF WATER FOn MICRO-ORGANISMS 67 



addition of soda crystals to ordinary gelatine-peptone, 

 with special reference to the development of the cholera 

 organism. It was found that slightly alkaline gelatine, 

 as usually recommended, was not suitable for the culti- 

 vation of the comma bacillus, but that gelatine to which 

 1 per cent, of soda crystals had been added gave ex- 

 cellent results, and greatly facilitated the detection of 

 the bacillus in f^ces in the presence of other organisms. 

 Aufrecht (' Centralblatt f. Bakt.' vol. xiii. p. 354) con 

 firms these observations on the favourable results ob- 

 tainable by this addition. (In this connection see also 

 p. 276.) 



Pohl ^ has also introduced modifications in the com- 

 position of the gelatine-peptone which he employed in 

 the examination of some marsh-water, whereby he was 

 able to isolate four new varieties, which whilst growing 

 luxuriantly in the modified medium hardly developed 

 at all, and were quickly crowded out by the other water 

 bacteria, in the ordinary gelatine-peptone. These suc- 

 cessful results were obtained by adding ammonium 

 carbonate to the culture medium in the proportion of 

 from 0*5 to 1 per cent. Pohl recommends that the 

 preparation of this ammonia-gelatine should be carried 

 out in the following manner : — The gelatine-peptone is 

 sterilised as usual, and mixed with a carefully sterilised 

 solution of ammonium carbonate ; this mixture may be 

 subsequently heated for half an hour in the water bath 

 to ensure absolute sterility, but if it is heated for longer 

 than this the greater part of the ammonium carbonate 

 is lost, and the gelatine moreover, being overheated, 

 solidifies less readily. 



The bacteriological examination of brewing waters 



^ ' Ueber Kultur und Eigenschaften einiger Sumpfwasser-BaciUen und 

 iiber die Anwendung aUcalischerNahrgelatine,' Centralblatt fur Bahterio- 

 logie, vol. xi,, 1892, p. 141. 



F 2 



