64 MICRO-ORGANISMS IN WATER 



quantities of a concentrated solution of sodium car- 

 bonate to the 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 : 



Quantity of sodium carbonate added to 10 c.c. of Number of colonies obtained 



ordinary slightly alkaline gelatine-peptone per A c.c. of water 



Without any addition ....... 475 



0-00504 gram sodium carbonate 1,140 



0-01008 , 2,976 



0-02016 

 0-03024 

 0-05040 

 0-07560 

 0-10080 

 0-15120 

 0-20160 

 0-30240 



2,486 



1,612 



1,302 



748 



348 



216 



74 







This table shows clearly the effect on the develop- 

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

 the introduction of O'Ol gram sodium carbonate caus- 

 ing the number of colonies found to be six times as 

 great as that revealed by using the ordinary gelatine. 

 Heinsch 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 tartai'ic acid added to 10 c.c. of ordinary Number of colonies obtained 



"slightly alkaline gelatine-peptone per \ c.c. of water 



Without any addition 406 



0*0028 gram tartaric acid 340 



0-0056 .,... . . 173 



0-0084 .. 19 . 



0-0112 11 



0-0140 6 



0-0224 



Thus with the increasing acidity of the medium the 

 number of colonies develo'ped steadily diminishes. 



