Kirchner — Bacteriological Examination of River Water. 285 
It will be seen from Table VIII that media with reaction 
+ 1.5 were best suited for the examination of water bacteria 
and it was the reaction of medium which was adopted through- 
out the work. 
The chief objections to the use of gelatin in quantitative 
work lie in the fact that it melts at body temperature, and 
that it is liquefied by certain bacteria. However, it is just 
this latter property which makes it useful in judging of the 
quality of water. In my own experience, I soon learned to 
distinguish the water collected from the various sources by 
the character of growth on the gelatin plate. In order 
to determine the relative proportion of liquefying bacteria 
developing at the time when the plate was usually counted, I 
made a number of estimations for each of the different 
sources from which the water was collected. In each case 
23-25 comparative counts were made, but for the purposes — 
of illustration an example from each group may be sufficient. 
(Table IX.) Adjoining the table is a summary showing the 
average of results (23 tests) from each of the different 
waters. 
TABLE IX. 
SHOWING RELATIVE PROPORTION OF LIQUEFYING COLONIES. 
Number of Colonies Av. per 
per 1 c.c. cent. of 
Source of Sample. * Liquefy- 
: ing Col- 
Total. |Liquefying Col. Anta: 
Drainage Canal, Lockport.......-++----- 209,000} 2,500 1.0% 1.5% 
Des Plaines R., Joliet...... ceeececencees 218,000} 4,000 2.0% 2.5% 
Illinois R., Peoria...... WESh wdide cede ney as 47,000} 500 1.0% 0.5% 
MIUIMOMS Bg GRATION s 366 Soo soles bie eee sean 4,900; 150 5.0% 4.0% 
Mississippi R., Grafton...........-----. 11,300} 540)" 4.0% 4.0% 
Ditamteetiad Wh: BIGOM, é< i sind a.cde dase ss 1,500, 190] 10.0%|| 10.0% 
Mississippi R., Hartford............ ..+- 2,600; 200 8.0% 9.0% 
Missouri R., Bellefontaine..........--.+- 9,100} 650 7.0% 7.0% 
Mississippi R., Chn. of Rocks, Intske.... 7,300} 550 8.0% 7.0% 
Mississippi R., Chn. of Rocks, East Shore. 2,100} 120 6.0% . 6.0% 
Mississippi R., Chn. of Rocks, WestShore.} 10,100) 500 5.0% 5.0% 
Reservoir, Chain of Rocks.........++-4+- 8,600} 180 5.0% 5.0% 
Tap, City LADOPAtory soa cscs sec'scceks 1,100 95 9.0%|| 11.0% 
The results as shown by the tables are relative and not 
absolute; the estimation was made on the third day of incu- 
