WATER ANALYSIS. 117 
placed thereon and the number of colonies in several of the 
square divisions counted, the average taken, and the 
Fic, 51.—Wolfhiigel’s apparatus for counting colonies of 
bacteria upon plates, 
number in the whole dish estimated. A lens is used in 
counting the colonies. 
Fic. 52.—Jeffer’s plate for counting colonies in circular 
dishes. The area of each division is 1 square centimeter. 
8 
