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