390 The Parasites of Civilisation. [July, 
sewerage. It is suggested by many engineers that the water- 
closets, the domestic sinks, the public urinals, &c., should 
discharge their contents into one set of sewers, whilst the 
surface-drainage is carried away by a distinct system. It 
must be admitted that this double system has some decided 
advantages : the sewage, properly so called, would be at all 
times much more nearly alike in strength and quantity, 
which would facilitate its treatment, whether by irrigation, 
filtration, or precipitation. Its value would be also much 
greater. On the other hand, the expense of the double 
system is a very serious consideration. The water from the 
street-gutters, though receiving nothing from the urinals and 
closets, will be far from clean, and its admission into the 
streams will be very doubtful. In manufacturing towns 
there are many waste liquids, — e.g., the rinsing- waters from 
dye-works, — which if run into the sewage will very much 
dilute it, but if allowed to pass into the rivers will greatly 
spoil their appearance. 
Lastly, it is sometimes found, even where the ordinary 
single system prevails, that the sewers require flushing 
to prevent solid matter from being deposited in parts where 
the gradient is insufficient. It is reasonable to suppose that 
this will be much more frequently the case in a sewer which 
carries faecal matters only, undiluted with surface water. 
Here, then, we should get back, occasionally at least, to 
that dilution of the sewage which was to be avoided by the 
double system. 
III. THE PARASITES OF CIVILISATION. 
(ijj/ 0 ET no galled jade wince! We are not about to 
discuss the “ social parasite ” — the schizomycete in 
human guise, who, by a necessity of his pathogenic 
nature, seeks to split up faiths, societies, empires, into seCts, 
cabals, and factions, just as his prototype splits up healthy 
cells and converts them into ptomaines. With such para- 
sites we have no concern. Our object is to view the vege- 
table and the infra-human animal world in its relation to 
