232 
reach of the river in which the bacterial action and attendant 
decay of the sewage ensues, are lengthened as the temperature 
falls, and we find in consequence an increase in the bacteria in 
the river water passing Havana which approximates fortyfold. 
The pulse in bacteria due to the sewage of Peoria which is 
found at Pekin during the summer, reaches Havana also, thirty- 
two miles below, as temperatures fall in the autumn. 
The averages of the number of colonies of bacteria found 
in the canal and river water at points from Bridgeport to Graf- 
ton during the period of analyses given in the first table are to 
be found in the following table, also taken from Jordan (’00). 
CHLORINE AND BACTERIA—DES PLAINES AND ILLINOIS RIVERS, 
BRIDGEPORT TO GRAFTON. 
Distance from | ; 
3 2 Chlorine (pts. | Number of col- 
Collecting Stations Preece per Saisan) onies per cm.® 
scala ove tiearanemAdaoonodcnoap.so5e fo) IIg.2 1,245,000 
COCK POLE cic custeteiitele tere eel eae 29 117.4 650,000 
aes EAN O Ren aera BEA Odes 0d 33 104.8 486,000 
OLMIS Merny seisiets artery nei ieeoeeoiats 57 68.1 439,000 
KO ETAW.AY cies csioscpovcis stsietseereaie eine ose efor 81 58.5 27,400 
War Salles a: csvsrcssnien morc emcn ies 95 46.1 16,300 
Jn GIN SeDAnOUOHEMOOea A nods bO0G cour 123 44.2 11,200 
Nisa Seppo osancorscansoboooad 159 40.9 3,660 
Wesley City ier s seceererieete creas 165 40.9 758,000 
PEK F 515 0: saya ltue ete clatetertetstnerensieien 175 38.4 492,600 
SEV EhiE eer oerogomaucocuacaGRdodlU 199 36.2 16,800 
Beards foyer seas beset 231 29.3 14,000 
Kampsville’ if... sis ciieictestetoieivetsl<tte= 288 22.9 4,800 
Grattondie 2 ily st amines eee eevee 319 18.3 10,200 
The chlorine content at the several points also appears in 
the table, and exhibits a steady decline from Chicago to the 
Mississippi River with a brief pause at Peoria. This decline 
expresses approximately the dilution which on an average the 
sewage undergoes during the low-water period. The flood 
season of the spring was not included in the period of analysis. 
From Ottawa to the mouth of the Illinois, as indicated by the 
chlorine, this dilution is about one third. 
The decrease in number of bacteria, while it may not coin- 
cide strictly with the completion of processes of decay still 
