From this point the President proceeded to speak of the increased toxical power of volatile compounds given off by neglected decomposed matter, and was thence led to dwell upon the dangers arising from decomposed substances in cesspools and in badly constructed drains. There was no doubt, he said, that in the sewering of towns want of experience in the construction of works had in some cases led to deposits in the sewers, and evil consequences had ensued; but it might be accepted as certain that in every case where the sewerage had been devised on sound principles, and where the works had been carried on under intelligent supervision, a largely reduced death-rate had invariably followed.

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.

That is to say, a man breathing pure air obtains, and he requires, 2,164 grains of oxygen per hour. In bad air he would, if breathing at the same rate, get little over 2,000 grains of oxygen an hour--that is, a loss of 5 per cent.; and this diminished quantity of oxygen is replaced with other, and in almost all cases, pernicious matters. The oxygen is the hard-working, active substance that keeps up the fire, cooks the food, and purifies the blood; and, of course, as the proportion of oxygen in the air breathed diminishes, the lungs must exert themselves more to obtain the necessary quantity of oxygen for carrying on the functions of life. If the air is loaded with impurities the lungs get clogged, and their power of absorbing the oxygen that is present in the air is diminished. An individual breathing this impure air must therefore do less work; or, if he does the same amount of work, it is at a greater expense to his system.

The influence of smoky town air on health is to some extent illustrated by the fact that the death-rate of twenty-three manufacturing towns, selected chiefly for their smoky character, averaged 21.9 per 1,000 in 1880; while the rural districts in the counties of Wilts, Dorset, and Devon, excluding large towns, averaged 17.7 per 1,000; and the deaths from the principal zymotic diseases in the towns were more than double those in the rural districts.

The President quoted the experiments of Mr. Aitkin, of Edinburgh, on the creation of fogs--that the vapor of water injected into air, from which particles had been strained out, was not visible; whereas as soon as foreign matter, such as dust, or smoke, or fumes, and especially fumes of sulphur, were introduced, the aqueous vapor condensed on the particles, and became visible as fog, and pointed out the fact that the barbarous method which we adopt for burning coal in this country adds to the dust the fumes which necessarily result from combustion, as well as a quantity of soot and tarry matter, a soot which assists in forming the black canopy which it is the fashion in England to consider the proper attribute of a large town.

He quoted the opinions of eminent scientific men to show that it was possible, under proper methods of burning coal, to lessen the intensity of fogs, and so to lessen materially the causes of ill-health, terminating in fatal disease of those subject to them. In dealing with the wide subject of the "general effect of sanitary conditions upon health," he gave some remarkable facts showing that sanitary work had reduced the death-rate of the European army in India from 60 per 1,000 to 16 per 1,000; that the deaths from tubercular disease in the army at home used to be 10 per 1,000--the sum total now of the total deaths from all causes in a time of peace--a reduction due to the improved hygienic conditions under which soldiers now live; that the death-rate in a certain part of Newcastle (now removed) used to be 54 per 1,000, and of the entire borough 26.1 so lately as seven years ago, while now it was 21.8; that in parts of London, where the people were ill-lodged and crowded, as in parts of Limehouse, Whitechapel, Aldgate, and St. Giles's, the death-rates were 50 per cent. above the death-rates in more open parts of the same districts, and that when proper dwellings were erected the death-rates fell from 50 in the 1,000 to not more than 20 per 1,000. He then spoke of the advantage arising to the health of the population generally by the new dwellings for artisans.