ime to the
walls of the sewer; and this slime must always be in a state of
decomposition, a constant source of offence and possible danger. The
only way to avert this danger is to give the sewer such a thorough
ventilation that the decomposition shall be rapid and safe, and that the
resultant gases shall be at once diluted with fresh air.

This may be measurably accomplished by the simple ventilation of the
sewer itself, through open-topped man-holes; but such ventilation is
less effective in the case of small sewers than of large ones. In the
case of either large or small sewers, it will be vastly increased if we
compel every householder who makes a connection with the sewer, to carry
a drain and soil pipe, nowhere less than four inches in diameter, from
the point of junction with the main line to the open air above the roof.
Where houses are near enough to make the use of a public sewer
advisable, the aggregate of these soil-pipes, having almost constantly
an upward current, will make such a draught upon the sewer, to be
supplied by a downward current through the man-hole covers, as will
maintain a perfect and continuous ventilation.

* * * * *

Important as it is to secure the proper arrangement and construction of
sewers and house-drains, it is still more important to provide for the
safe disposition of the sewage.

We must begin at the outset with the understanding that all sewage
matters not only are of no value to the community, but that it will cost
money to get rid of them.

There is hardly an instance, after all the efforts that have been made,
of the _profitable_ disposal of the outflow of public sewers. The
_theoretical_ value of the wastes of human life is very great, but the
cost of any method for utilizing them seems at least equally great. The
question of cost is so much more important (to the community) than the
question of agricultural value, that the practical thing to do is to
make such disposition as will cost the least, while fully meeting the
best sanitary requirements.

So far as village sewage is concerned, there are three means open for
its disposal: to discharge it into running water or into deep
tide-water, to use it for the surface irrigation of land, or to
distribute it through sub-irrigation pipes placed at little distance
below the surface of the soil. Experiments are being made with more or
less promise of success in the direction of the chemical tre