sibility of any nuisance being committed.

_Treatment of sewage on land._

If no stream suitable for the reception of sewage is available, then the
sewage must in some way be treated on land before it passes into the
nearest watercourse. For the second fundamental principle about the
treatment of sewage is that of all places the action of putrefactive
bacteria is most energetic in the surface soil and that it is there that
the organic matter of sewage can be most rapidly accomplished.
Experiments already referred to have shown not only this, but also that
their activity is most noticeable in the surface layers of the soil and
that their action continues for scarcely two feet downward, and it is
customary to assume that the largest amount of work done is accomplished
in the top twelve inches. Further than this, it has been established
that in order to persuade the bacteria involved to do their work as
promptly as possible, the application of sewage to any particular
locality should be made intermittent; that is, that a resting period
should be given to the bacteria between successive applications of
sewage.

For example, one can recall without difficulty the conditions on the
ground at the back of the house where the kitchen sink-drain commonly
discharges. At the beginning of summer perhaps a rank growth of grass
starts up vigorously in the vicinity, and the path of the surface drain
can be traced by the heavy vegetation along the line of the drain. If
the slope of the surface away from the house is considerable, no other
effect may be noticed through the season, since the surface slope
carries away the sewage, spreading it out over the ground so that the
soil really has a chance to breathe between successive doses. But if the
ground is flat, it will be remembered that before many weeks the sewage
ceases to sink into it; the ground becomes "sewage-sick," as they say in
England, and a thick, dark-colored pool of sewage gradually forms, which
smells abominably. If a piece of hose a dozen feet long had been
attached to the end of the drain and each day shifted in position so
that no particular spot received the infiltration two days in
succession, it is probable that no such pondage of sewage would occur,
but that the mere intermittency of the application thereby secured would
permit the successful disposal of this sink waste throughout the season.

The same effect is to be noted in some cesspools where, because of the