EPFECE. OF POLLUTIONS. 59 
But Parliament and the public are becoming more and 
more alive to the necessity for purifying our streams, not 
merely for the sake of the fisheries, but in the interests of 
public health ; while manufacturers and others are slowly 
recognising the fact that they are often throwing away 
valuable material, capable of being turned to profitable 
account, when they blindly pour their refuse into the 
streams. 
Pollutions are of two kinds, liquid and solid. The 
former, by chemical action, are most deadly and insidious, 
destroying the oxygen in the water which the fish breathe, 
and actually injuring their gills or breathing organs ; the 
latter choke by mechanical action, clogging the gills and 
suffocating the fish. Solid pollutions have an even more 
serious effect upon the fisheries by destroying the spawn- 
ing beds, which become smothered with a thick muddy 
deposit, in which the fish will not spawn, or, even if they 
did, the eggs would not develop. China-clay works, mines, 
and collieries, are notable offenders in this respect. But it is 
perfectly practicable, by collecting in settling tanks or 
catch pits the refuse water which holds these matters in sus- 
pension, to allow the sediment to fall to the bottom, when 
the water will flow off practically clean. The sediment or 
“sludge ” itself, in most cases, is capable of being converted 
into bricks, or applied to some similar purpose ; and, even 
if it is not, the cost of carting it away to a spot where it 
will do no harm would soon be repaid by the good done to 
the fisheries by keeping it out of the river. 
Chemical poisons in solution are more difficult to deal 
with, but they are so much more deadly and far-reaching 
in their effects that there is still less reason for hesitation in 
compelling their diversion from the rivers, especially as 
they are, with probably hardly an exception, capable of 
