Where measures for drainage and cleansing, such as have
been described, have not hitherto been introduced, the free use
of lime, chloride of lime, or muriate of zinc, and the evolution
of small quantities of chlorine and nitrous acid in the apart-
ments subject to their emanations will be found beneficial.
But these alone do not give permanent satisfaction. The mass
of corruption ought to be removed. With every fall of the
barometer the vicinity may be flooded by the escape of offen-
sive emanations as they are more or less relieved from
atmospheric pressure.
Where a large extent of drains is loaded with decomposing
debris it is important to have two apertures formed, fresh air
being permitted to enter by one, and offensive gases to escape
by the other. A chimney placed over the latter and the intro-
duction of a small fire when necessary secures the discharge
and decomposes the products evolved.
These brief memoranda, if connected with the elementary
explanations given in the preceding pages, will show how
largely chemical considerations are associated with many
questions affecting the duration of human life. They might
be extended in reference to the influence of Exerciae^ Occu-
pations, the origin of Disease, the iti^vxeiie^ qH ^^ \cksA «^
the body, and the action and deveVopTCi^ivX. ^'vCavo. \Jftfc ^>n>^'^
system of electncsl forces that axe p^TV^twaJ^'i V». o^et-ascvss^-



190 CHEMICAL AGENCIES AFFECTING LIFE.
