ile increases, and the population becomes
as dense as it is in some towns and cities, the disposal of the human
waste products becomes a question of vast importance, and the proper,
as well as the immediate and final, disposal of sewage becomes a
serious sanitary problem.

It is evident that sewage must be removed in a thorough manner,
otherwise it would endanger the lives and health of the people.

The dangers of sewage to health are:

(1) From its offensive odors, which, while not always directly
dangerous to health, often produce headaches, nausea, etc.

(2) The organic matter contained in sewage decomposes and eliminates
gases and other products of decomposition.

(3) Sewage may contain a large number of pathogenic bacteria (typhoid,
dysentery, cholera, etc.).

(4) Contamination of the soil, ground water, and air by percolation of
sewage.

The problem of sewage disposal is twofold: (1) immediate, viz., the
need of not allowing sewage to remain too long on the premises, and
its immediate removal beyond the limits of the city; and (2) the final
disposition of the sewage, after its removal from the cities, etc.

=Modes of Ultimate Disposal of Sewage.=--The chief constituents of
sewage are organic matter, mineral salts, nitrogenous substances,
potash, and phosphoric acid. Fresh-mixed excrementitious matter has an
acid reaction, but within twelve to twenty hours it becomes alkaline,
because of the free ammonia formed in it. Sewage rapidly decomposes,
evolving organic and fetid matters, ammonium sulphide, sulphureted and
carbureted hydrogen, etc., besides teeming with animal and bacterial
life. A great many of the substances contained in sewage are valuable
as fertilizers of soil.

The systems of final disposal of sewage are as follows:

(1) Discharge into seas, lakes, and rivers.
(2) Cremation.
(3) Physical and chemical precipitation.
(4) Intermittent filtration.
(5) Land irrigation.
(6) "Bacterial" methods.

_Discharge into Waters._--The easiest way to dispose of sewage is to
let it flow into the sea or other running water course. The objections
to sewage discharging into the rivers and lakes near cities, and
especially such lakes and rivers as supply water to the
municipalities, are obvious. But as water can purify a great amount of
sewage, this method is still in vogue in certain places, although it
is to be hoped that it will in the near future be superseded by more
proper met