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. 



Source of Sample. 



Number of Colonies 

 per 1 c.c. 



Total. Liquefying Col. 



Av. per 

 cent, of 

 Liquefy- 

 ing Col- 

 onies. 



Drainage Canal, Lockport 



Des Plaines R. , Joliet 



Illinois R., Peoria 



Illinois R. , Grafton 



Mississippi R. , Grafton 



Mississippi R.j Alton 



Mississippi R., Hartford 



Missouri R , Bellefontaine 



Mississippi R., Chn. of Rocks, Intake 



Mississippi R., Chn. of Rocks, East Shore. 

 Mississippi R., Chn. of Rocks, West Shore. 



Reservoir, Chain of Rocks 



Tap, City Laboratory 



1.5% 

 2.5% 

 0.5% 

 4.0% 

 4.0% 



10.0% 

 9.0% 

 7.0% 

 7.0% 

 6.0% 

 5.0% 

 5.0% 



11.0% 



The results as shown by the tables are relative and not 

 absolute ; the estimation was made on the third day of incu- 



