1 885-1 The Composition of Sewage. 389 
than on other days, and requires an extra share of at- 
tention. 
The question has often been raised whether there is any 
marked difference between the sewage of a “ closetted ” 
town and one where a part, larger or smaller, of the popu- 
lation make use of the old-fashioned cesspools, or of dry 
earth-closets and similar appliances. Certain authorities, 
on the faith of their analyses, have maintained that there is 
little or no difference in the strength of the sewage. Care- 
ful consideration will show that this is scarcely possible. It 
may be at once admitted that the liquid excrements of man, 
and of all analogous animals, contain a larger proportion of 
nitrogenous matter than do the solid excreta. But in a 
closetted town the whole of the excrements of the popula- 
tion, liquid and solid, find their way into the sewers, and 
thence into the river. In an unclosetted town not merely 
the solid, but a large part of the liquid excretions are dis- 
charged into the cesspools, dry closets, &c. Very frequently 
also, in small straggling towns, public urinals, if they exist 
at all, are not connected with the sewers. Thus the water 
running in the latter consists to a great extent of soap- 
suds, the washings of plates and dishes, and, in short, what 
is technically known as “ slops.” I do not see, therefore, 
how it is possible for the sewage of an unclosetted town, 
other things being equal, to be as rich in nitrogenous matter 
as that of a thoroughly closetted town. 
A very important consideration is the water-supply, known 
and unknown. By the known supply I mean the average 
quantity per head of the population served out from the 
water-works. By the unknown I mean the quantity which 
leaks into the sewers from other sources. Where the 
sewerage system lies in a wet sub-soil, with many ground- 
springs, and where the sewers themselves are not water- 
tight, the flow of sewage in dry weather may rise to 
100 gallons per head of the population per twenty-four 
hours, whilst in towns where the water-supply is scanty, 
or where the sewers are well made, it may fall as low as 
20 gallons. 
Another very important distinction is the space covered 
by a town in respeCt to its population. Where the streets 
are wide, where there are few persons to a house, and where 
there are many gardens, paddocks, vacant spots of building 
ground, &c., the sewage, especially in wet weather, is so 
much diluted that it loses all its distinguishing properties, 
and is little worse than ditch-water. 
This brings us to the question of single or double 
