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) 



Medium. 



Days' Count. 



Nahrstoflf agar 



Nahrstoff peptone agar 



Peptone agar 



Meat agar 



Plain agar 



Regular agar 



Nahrstoff glycerin agar 

 Nahrstoff meat agar . . . 



Meat gelatin 



Peptone gelatine 



Standard gelatin 



Plain gelatin 



Nahrstoff gelatin 



60 



22 I 

 16 I 



13 



10 i 



9 : 

 10 



7 



19 ; 

 12 



6 I 

 6 t 



78 

 26 

 22 

 16 

 13 



24 



12 

 9 



8S 

 28 



23 

 17 

 14 



26 

 20 



95 

 30 



24 

 17 

 14 



10 

 26 

 20 

 13 

 13 

 13 



99 

 30 

 24 

 17 

 14 

 II 

 II 

 10 

 26 

 20 

 13 

 13 

 13 



100 

 30 

 24 

 17 

 14 

 II 

 II 

 10 

 26 

 20 

 13 

 13 

 13 



Whipple (Whipple, 1902) has shown that not only 

 the particular kind of gelatin used, but its exact physical 

 condition as affected by steriHzation 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. 



