QUANTITATIVE EXAMINATION OF WATER 45 



AVERAGE RELATIVE NUMBER OF BACTERIA ON PEP- 

 TONE AGAR WITH DIFFERENT PEPTONES 



(GAGE AND ADAMS, 1904) 



The same authors showed that the composition of 

 the water used exercised a marked selective action upon 

 the development of bacteria. Agar made up with 

 sewage permitted a maximum growth of sewage bacteria 

 and showed no colonies when inoculated with filtered 

 city water. On the other hand agar made up with city 

 water showed 100 per cent of the bacteria present in 

 city water and river water, three-quarters of those 

 present in sewage and less than half of those present 

 in sewage effluents. 



Hesse (1904) found that the number of bacteria 

 developing on Nahrstoff agar varied with the composi- 

 tion of the glass tubes in which the media had previously 

 been sterilized. The more soluble glasses yielded 

 sufficient alkali to the medium to inhibit four-fifths of 

 the bacteria present in certain cases. 



All these facts make it evident that only the strictest 

 adherence to a standard method can ensure comparable 

 results; the ordinary nutrient gelatin or agar should 

 then in all practical sanitary work be made up from 

 distilled water, meat infusion, peptone and gelatin or 

 agar, in exact accordance with the directions of the 

 Standard Methods Committee. 



