pter. As the venous blood in this unchanged state is unfit
to excite or sustain the action of the brain, the mental functions
become impaired, and death speedily ensues, as in the case of a number
of persons breathing a portion of confined air, or inhaling the fumes of
charcoal. On the other hand, if oxygen gas be inhaled instead of common
air, the blood becomes too much oxygenated, and, as a consequence, the
brain is unduly stimulated, and an intensity of action bordering on
inflammation takes place, which also soon terminates in death.

These are extreme cases, I admit; but their consequences are equally
remarkable and fatal. The slighter variations in the state of the blood
produce equally sure, though less palpable effects. Whenever its
vitality is impaired by breathing an atmosphere so vitiated as not to
produce the proper degree of oxygenation, the blood can only afford an
imperfect stimulus to the brain. As a necessary consequence, languor and
inactivity of the mental and nervous functions ensue, and a tendency to
headache, fainting, or hysteria makes its appearance. This is seen every
day in the listlessness and apathy prevalent in crowded and
ill-ventilated school-rooms, and in the headaches and liability to
fainting which are so sure to attack persons of a delicate habit, in the
contaminated atmospheres of crowded theaters, churches, and assemblies
of whatever kind. The same effects, although less strikingly apparent,
are perhaps more permanently felt by the inmates of cotton manufactories
and public hospitals, who are noted for being irritable and sensitive.
The languor and nervous debility consequent on confinement in
ill-ventilated apartments, or in air vitiated by the breath of many
people, are neither more nor less than minor degrees of the process of
poisoning, which was particularly explained in the preceding chapter,
while treating upon the philosophy of respiration.

That it is not real debility which produces these effects, is apparent
from the fact, that egress to the open air almost instantly restores
activity and vigor to both mind and body, unless the exposure has been
very long. There is an interesting but fearful illustration of the truth
of this statement at the 96th page of this work, to which I beg leave to
refer. Where the exposure has been very long continued, more time is of
course required to re-establish the exhausted powers of the brain.
Indeed, we may not, in such cases, hope for comp