porous
earthenware pipes or ordinary drain tile. The drains must not be
impermeable or closed, and sewers are not to be used for drainage
purposes. Sometimes open, V-shaped pipes are laid under the regular
sewers, if these are at the proper depth.

By subsoil drainage it is possible to lower the level of ground water
wherever it is near or at the surface, as in swamps, marsh, and other
lands, and prepare lands previously uninhabitable for healthy sites.

FOOTNOTES:

[10] Humus is vegetable mold; swamp muck; peat; etc.--EDITOR.

[11] A leak in a gas main, allowing the gas to penetrate the soil,
will destroy trees, shrubbery, or any other vegetation with which it
comes in contact.--EDITOR.

[12] Town and village paving plans will benefit by knowledge of the
recent satisfactory experience of New York City authorities in paving
with wood blocks soaked in a preparation of creosote and resin. As
compared with the other two general classes of paving, granite blocks,
and asphalt, these wood blocks are now considered superior.

The granite blocks are now nearly discarded in New York because of
their permeability, expense, and noise, being now used for heavy
traffic only.

Asphalt is noiseless and impermeable (thereby serving the "double
sanitary purpose" mentioned by Dr. Price).

But the wood possesses these qualities, and has in addition the
advantage of inexpensiveness, since it is more durable, not cracking
at winter cold and melting under summer heat like the asphalt; and
there is but slight cost for repairs, which are easily made by taking
out the separate blocks.

These "creo-resinate" wood blocks, recently used on lower Broadway,
Park Place, and the congested side streets, are giving admirable
results.--EDITOR.

CHAPTER II

=Ventilation=

=Definition.=--The air within an uninhabited room does not differ from
that without. If the room is occupied by one or more individuals,
however, then the air in the room soon deteriorates, until the
impurities therein reach a certain degree incompatible with health.
This is due to the fact that with each breath a certain quantity of
CO2, organic impurities, and aqueous vapor is exhaled; and these
products of respiration soon surcharge the air until it is rendered
impure and unfit for breathing. In order to render the air pure in
such a room, and make life possible, it is necessary to change the air
by withdrawing the impure, and substituting pure air from the