39° Observations on Polluted Waters. [July, 
mouth of a sewer, but on careful examination I have rarely 
failed to note some dead specimens floating on the surface. 
It is very plain, on theoretical considerations, that sewage, 
or water containing a large proportion of sewage, must be 
fatal to fishes as a medium for constant residence. We 
know that they breathe not the oxygen existing in combina- 
tion with hydrogen in the water, but the free oxygen which 
has been dissolved in the water. It has been found that fish 
quickly perish in water which has been boiled and allowed 
to cool in a closed vessel without agitation. Now in sewage, 
and in sewage-polluted river- water, it is analytically demon- 
strable that the proportion of free oxygen is very much 
reduced. The various kinds of organic matter undergoing 
rapid changes use up the available oxygen, and unless 
aeration is effected by rapid motion, or by the aCtion of 
water-vegetation, fish are in the same condition as a man 
would be if placed in a highly rarefied atmosphere. In con- 
sequence they must either retire from the danger or ulti- 
mately perish. 
It must not be supposed that this deprivation of free 
oxygen is the only reason why fish are unable to survive in 
polluted waters ; but it is a cause readily demonstrable, and 
one which cannot fail in its aCtion. But many of the agents 
employed by individuals or by communities, for lessening or 
preventing the offensiveness of sewage, render it even more 
destructive to fish. It is known that not a few sewage pro- 
cesses employ lime, not merely to correct the acidity some- 
times met with in industrial waste waters, but as a positive 
precipitant. I know of a case where 16 tons of quick- 
lime have been put daily into the sewage of a single town, 
unaccompanied by any corresponding dose of an acid or of 
an acid salt. In all such cases the effluent water has a 
faint alkaline reaction ; it is, in faCt, weak lime-water. Now 
everyone surely knows that lime is hostile to fish, and indeed 
to water-vegetation. By putting a few lumps of quick- 
lime into a stream, poachers often succeed in killing the fish 
for a considerable distance. We must therefore readily 
admit that where the introduction of lime is continuous, 
fish cannot prosper. It may be argued that lime-water on 
exposure to the air becomes harmless, all its lime being 
converted, by the carbonic acid of the air, into calcium 
carbonate, in which state it is very sparingly soluble ; but 
when the quantity of lime-water introduced into a slowly- 
flowing river is great and continuous, the water must travel 
for many miles before, this conversion can be effected. 
Hence I can but advise riparian proprietors, lessees of 
