mbining with the barnyard drain, is carried into the stream near
by. The very idea of drinking such filth is nauseating in the extreme.
It is common for small slaughter-houses to be built on the side of a
stream, so that the offal, carrion, and refuse of the place may be
carried off without effort on the part of the owner, and there are a
number of such places where brooks, used as places of deposit for
slaughter-house refuse, discharge directly into the reservoirs of water
works.

But this sort of animal refuse is not the most serious pollution. The
leachings and washings from privies and cesspools, carrying, as they do,
germs of contagious diseases, are most to be dreaded, and when a privy
(with no vault underneath) is built on the side of a steep ravine and is
so located that the natural drainage of the sidehill on which it is
built cannot help but run around and through the building, then the
pollution of the stream in the gulley is not only direct and inevitable,
but of a deadly sort (see Fig. 36). Fortunately, the germs thus carried
into the stream suffer the vicissitudes of all life exposed to the
attacks of hostile forces.

At the time of freshets the streams carry mud in abundance, which mud is
continually settling out of the water as opportunity offers, and with
this settlement of mud there occurs also the settlement of the germs.
Also the pathogenic or disease-producing germs are usually weaker and
more susceptible than the putrefactive and other organisms which are
found in the water in great abundance after any rain storm, and which
tend to inhibit or destroy the pathogenic germs. But some will survive,
and, with favoring conditions, may pass through the water-pipe to the
house, causing sickness, if not death.

[Illustration: FIG. 36.--Stream draining a privy.]

Any inspection of the watershed, therefore, should look to the
elimination of the dangers above described, and to the location of barns
and barnyards, pig-pens and poultry yards, privies and cesspools, so
that no direct drainage into the stream shall be possible.

It is out of the question for any surface water-supply to be pure, since
the mere fact of the passage of water over the soil inevitably results
in the collection of organic matter; and it is no exaggeration to say
that the time will inevitably come in this country, as it has already in
Germany, when no surface supply will be considered satisfactory unless
the water is filtered. The on