64 



MICRO-ORGANISMS IN WATER 



quantities of a concentrated solution of sodium car- 

 bonate to tlie gelatine-peptone, and the effect produced 

 thereby on the development of water-microbes. The 

 water selected for experiment was abstracted from the 

 Elbe below Hamburg and Altona. As this water con- 

 tains a very large number of microbes it was diluted 

 with distilled water, and the figures given below have 

 reference to this diluted water. The following table 

 shows the results obtained : — 



This table shows clearly the effect on the develop- 

 ment of the water bacteria of the addition of this alkali^ 

 the introduction of 0*01 gram sodium carbonate caus- 

 ing the number of colonies found to be six times as 

 great as that revealed by using the ordinary gelatine. 

 Eeinsch has also experimented on the effect of adding 

 varying quantities of acid to the ordinary gelatine, and 

 his results are recorded in the following table : — 



Quantity of tartaric acid added to 10 ex. of ordinary Number of colonies obtained 



slightly alkaline gelatine-peptone per i c.c. of water 



Without any addition 406 



0*0028 gram tartaric acid ...... 340 



0-0056 



173 



19 



11 



6 







Thus with the increasing acidity of the medium the 

 number of colonies developed steadily diminishes. 



