by multiplying, exert a very marked influence
upon the health by the possible spread of infectious diseases. Sewage
pollution of the soils and of the source of water supply is a matter
of grave importance, and is one of the chief factors of high
mortality in cities and towns.

_Interment of Bodies._--The second cause of soil contamination is also
of great importance. Owing to the intense physicochemical and organic
changes taking place within the soil, all dead animal matter interred
therein is easily disposed of in a certain time, being reduced to the
primary constituents, viz., ammonia, nitrous acid, carbonic acid,
sulphureted and carbureted hydrogen, etc. But whenever the number of
interred bodies is too great, and the products of decomposition are
allowed to accumulate to a very great degree, until the capacity of
the soil to absorb and oxidize them is overtaxed, the soil, and the
air and water therein, are polluted by the noxious poisons produced by
the processes of decomposition.

_Introduction of Various Foreign Materials and Gases._--In cities and
towns various pipes are laid in the ground for conducting certain
substances, as illuminating gas, fuel, coal gas, etc.; the pipes at
times are defective, allowing leakage therefrom, and permitting the
saturation of the soil with poisonous gases which are frequently drawn
up by the various currents of ground air into the open air and
adjacent dwellings.

=Influence of the Soil on Health.=--The intimate relations existing
between the soil upon which we live and our health, and the marked
influence of the soil on the life and well-being of man, have been
recognized from time immemorial.

The influence of the soil upon health is due to: (1) the physical and
chemical character of the soil; (2) the ground-water level and degree
of dampness; (3) the organic impurities and contamination of the soil.

The physical and chemical nature of the soil, irrespective of its
water, moisture, and air, has been regarded by some authorities as
having an effect on the health, growth, and constitution of man. The
peculiar disease called cretinism, as well as goitre, has been
attributed to a predominance of certain chemicals in the soil.

The ground-water level is of great importance to the well-being of
man. Professor Pettenkofer claimed that a persistently low water level
(about fifteen feet from the surface) is healthy, the mortality being
the lowest in such places; a persistently