Evidence of this fact he adduced from the history of Newcastle, for in the ten years beginning in 1867 the death-rate was 27.6, while in the ten years ending 1881 (during which there had been improved sewerage in operation) the death-rate was only 23, while in 1881 it was only 21.7. He instanced the like results in Munich, where the entire fever 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.