mortality sank from 24.2 in the period when there were no regulations
in regard to cleanliness to 8.7 when the sewerage was complete, at
Frankfort-on-the-Main, at Dantzic, and at Hamburg, where similar results
obtained of a heavy zymotic mortality previous to the sewering of the
cities, and a lighter mortality on the completion of the works.

These results were set forth in figures, and after dealing with
the beneficial results of purifying the air of towns by the rapid
abstraction of refuse matter, he passed on to review "other fertile
causes of mischief" in poisoning the air of towns, the chief of these
being horse manure, the dust of refuse, and smoke.

On this subject he quoted Dr. Angus Smith, who in his "Contributions to
the Beginnings of a Chemical Climatology," shows that the air in the
middle of the Atlantic Ocean, on the sea-shore, and on uncontaminated
open spaces, commands the greatest amount of oxygen; that at the tops of
hills the air contains more oxygen than at the bottom; and that places
where putrefaction may be supposed to exist are subject to a diminution
of oxygen.

For instance, a diminution of oxygen and an increase of carbonic acid is
decidedly apparent in crowded rooms, theaters, cowhouses, and stables.
It is well known that oxygen over putrid substances is absorbed, while
carbonic acid and other gases take its place; and hence all places near
or in our houses which contain impurities diminish the oxygen of the
air. The average quantity of oxygen in pure air amounts to 21 parts out
of 100. In impure places, such, for instance, as in a sleeping-room
where the windows have been shut all night, or in a lecture-theater
after a lecture, or in a close stable, the oxygen has been found to be
reduced to as little as 20 parts in 100.