an this renders the atmosphere stuffy and unhealthy. It is generally
admitted that an average adult breathes out from 20 to 30 cubic inches
of steam and vitiated air per minute, or, as Dr. Arnott says, a quantity
equal in bulk to that of a full-sized orange. This vitiated air and
steam is respired at a temperature of 90 deg. Fahr.; and therefore, by
reason of this heat, it immediately ascends to the ceiling, together
with the heat and carbonic acid given off from the pores of the skin.
This fact, by the bye, can be clearly demonstrated by placing a person
in the direct rays from a powerful limelight or electric lamp, and thus
projecting his shadow sharply on a smooth white surface. It will be
observed that from every hair of the head and beard, and every fiber of
his clothing, a current of heated air in rapid movement is passing
upward toward the ceiling. These currents appear as white lines on the
surface of the wall; the cause probably being that the extreme
rarefaction of the air by the heat of the body enables the rays of light
to pass through them with less refraction than through the denser and
more moist surrounding cold air. An adult makes, on an average, about 15
respirations per minute, and therefore he in every hour renders to the
atmosphere of the room in which he is staying from 10 to 15 cubic feet
of poisonous air. This rises to the ceiling line, if it is not
prevented; and thus vitiates from 100 to 150 cubic feet of air to the
extent of 1 per cent, in an hour. General Morin thought that air was not
good which contained more than 1/2 per cent, of air which had been exhaled
from the lungs; and when we consider how dangerous to health these
exhalations are, we must admit that he was right in his view. Therefore
in one hour the 15 foot by 12 foot room is vitiated to more than 2 feet
from the ceiling by one person to the extent of 1/2 per cent., and it will
be vitiated by two persons to the extent of 1 per cent, in the same
time.

It must be remembered here that the degree of diffusion of the vitiated
air into the lower fresh air contained in the remaining 8 feet of the
height of the room depends very materially on the difference of
temperature between these upper and lower strata and the movements of
air in the room. The heavy poisonous vapors and gases fall into and
diffuse themselves among the fresh air of the lower strata--very readily
if they are nearly the same temperature as the upper, but scarcely at
a