44 ELEMENTS OF WATER BACTERIOLOGY 



existed for most water bacteria and that a devia- 

 tion either way decreased the number of colonies 

 developing. 



TABLE SHOWING PERCENTAGES OF BACTERIA DEVEL- 

 OPING ON MEDIA OF DIFFERENT COMPOSITIONS 



(GAGE AND PHELPS, 1902) 



Whipple (Whipple, 1902) has shown that not only 

 the particular kind of gelatin used, but its exact physical 

 condition as affected by sterilization and other previous 

 treatments, will materially affect the results obtained. 

 Gage and Adams (1904) found marked differences in 

 counts as the result of the use of the two best-known 

 commercial peptones. A long series of waters plated 

 on agar made up with Merck's and Witte's peptones, 

 respectively, showed the average relative results in the 

 table on page 45. 



