230 



flood (as in September) concentrating the sewage and at the 

 same time favoring the development of the plankton. 



That the sewage of Chicago is quite thoroughly rotted out 

 before it enters the Illinois at La Salle, and that the contribu- 

 tions from Peoria are also well advanced in decay before they 

 reach Havana have been demonstrated by the chemical and 

 bacteriological examinations made at the instigation of the 

 Sanitary District of Chicago apropos to the opening of the 

 drainage canal. The full results of this work have not as yet 

 been published, but from the data published by Prof. A. W. 

 Palmer ('97) from the analyses of the Chemical Survey and 

 from the preliminary report of Jordan ('00) upon the bac- 

 teriological examination it is evident that the nitrogenous 

 matters of the Chicago sewage were in process of rapid oxida- 

 tion in the upper reaches of the Illinois and Michigan canal 

 near Lockport; that this process was largely completed before 

 the canal waters entered the river at La Salle; and that the Pe- 

 oria pulse of sewage is, during the summer months at least, well 

 decayed before it reaches Havana, though in colder weather, 

 w^hen decay is less rapid, the sewage is not so well oxidized and 

 the bacteria are more abundant than during the summer at 

 this point. The following table, which has been made up from 

 the averages in Palmer, '97, exhibits to some extent these facts 

 in tabular form. The increase in nitrates and decrease in free 

 ammonia unite in indicating the extent to which decay has 

 progressed. 



*Average July 23— Dec. 29, 1896. 



The influence of the sewage of Peoria upon conditions at 

 Havana, owdng to temperature changes, is not uniform 



