y the physical senses that
point at which the human organism suffers from insufficient ventilation.
Some years ago, Dr. Angus Smith built an air-tight chamber or box in
which he allowed himself to be shut up for various lengths of time in
order to analyze his own sensations on breathing vitiated air. He found
that, far from being disagreeable, the sensation was pleasurable, and he
says, "There was unusual delight in the mere act of breathing," although
he had remained in the chamber nearly two hours. On another occasion he
stayed in more than two hours without apparent discomfort, although
after opening the door, persons entering from the outside found the
atmosphere intolerable. He placed candles in the box, which were
extinguished in a hundred and fifty minutes, and a young lady, who was
interested in the experiment, going into the box as the candles went
out, breathed it for five minutes easily; she then became white, and
could not come out without help.

Nor is it possible to conclude from the experiments and observations
cited that the body remains indifferent to polluted air until the latter
has reached a certain definite saturated condition. There can be little
doubt but that a degree of pollution far short of that necessary to
produce death has a weakening effect on the human organism, and that by
means of the increased functional activity of other organs doing work
intended for the lungs the resistance to disease is much impaired. Life
is a continual struggle of the bodily tissues against the attacks of the
micro-organisms and their tendencies to destroy life; hence inadequate
ventilation or any other condition which interferes with the normal
action of the organs of the body causes weakness and affords opportunity
for the attack of some disease-producing germ. It stands to reason that
an individual whose lung tissues have become soft and incapacitated must
be more liable to succumb to disease than another whose lung capacity is
large and whose blood has been continually and sufficiently oxygenated.

Perhaps no more impressive proof of this is seen than in the ravages of
consumption, which is so prone to attack those whose vitality is
diminished by living in unhealthy and unventilated cellars or in crowded
tenements. Statistics are very definite on the subject of tuberculosis
among Indians, who rarely suffer from the disease when living in tents
or on the open prairie, but when they become semi-civilized and cr