160 



THE AMEBIC AN NATURALIST 



[Vol. LIV 



the river and on some of the animal and vegetal life. 

 This study was made in 1912 when the pollution was at 

 its maximum and during the period when molluscan life 

 had disappeared from the upper part of the river below 

 the lower falls. The dissolved oxygen in the lower river, 

 below the trunk line sewer, in July and August when the 

 temperature was high and the water low, varied from 5 

 to 41 per cent, of saturation. The water at the bottom of 

 the river almost always contained less oxygen than that 

 at the surface. This condition prevailed to within a short 

 distance of the mouth of the river when the reverse was 

 true, this change being due to the backflow of the well- 

 oxygenated water from Lake Ontario. Near the east side 

 trunk sewer, which is about half a mile below the lower 

 falls, the percentage of saturation varied from 5 to 60 

 between July 1 and August 13. On August 13, the per- 

 centage of saturation between the east side trunk sewer 

 and a point two and a half miles from the lake (a distance 

 of about three miles) did not exceed five per cent. This 

 area includes the shores examined for the Mollusca. 

 The percentage of dissolved oxygen saturation was usu- 

 ally higher at the surface than at the bottom of the river, 

 the heavier parts of the sewage falling to the bottom and 

 forming sludge banks. The percentage of dissolved oxy- 

 gen also did not vary directly with the amount of evident 

 pollution, for on a day in July when the most disagree- 

 able conditions existed for a mile and a half below the 

 east side outlet the dissolved oxygen at the surface varied 

 from 40 to 70 per cent. 



A study of the plankton of the river indicated that 

 near the source of pollution, 5 J miles above the mouth of 

 the river, there were on the average in July and August, 

 1,650,000 bacteria, 156 algae, 209 Protozoa, and 57 Crus- 

 tacea and Rotifers per cubic centimeter. At the mouth 

 of the river the figures for these organisms per c.c. stood 

 as follows: 67,000; 363; 77; 233. It is unfortunate that 

 no discrimination was made between the foul water algae 

 and protozoa and those normally inhabiting pure water, 



