STVDV OF WATER. 433 



TABLE ILLXTSTBATING THE PROPOETION BETWEEN THE EE- 

 STJLTS OBTAINED BY THE USE OP GELATIN AND AGAE-AGAK 

 IN QUANTITATIVE BACTEEIOLOGICAL ANALYSIS OP WATEE. 

 EESULTS EECOEDED AEE THE NUMBEE OP COLONIES THAT 

 DEVELOPED FEOM THE SAME AMOUNT OP WATEE IN EACH 

 SERIES.' 



Nttmbek of Colonies fkom Wateb that developed upon— 



Throughout this part of the work it is to be borne 

 in mind that when one refers to plates it is not to a 

 set, as in the isolation experiments, but to a single 

 plate. 



Method of Counting the Colonies on Plates. 

 — For convenience in counting colonies on plates or in 

 tubes, it is customary to divide the whole area of the 

 gelatin occupied by colonies into smaller areas, and 

 either count all the colonies in each of these areas and 

 add the several sums together for the total ; or to count 

 the number of colonies in each of several areas, ten or 

 twelve, take the mean of the results and multiply this 

 by the number of areas containing colonies. 



1 I am indebted to Dr. James Homer Wright, Thomas Scott Fellow in 

 Hygiene (1892-93), University of Pennsylvania, for the results presented in 

 this table. 



