poisoned with carbonic acid, and starved for want of oxygen.

Whenever oxygen unites with carbon to form carbonic acid, or with
hydrogen to form water, heat is generated Thus it is that a land of
combustion is constantly going on in the capillaries all over the body.
It is this burning of the decaying portions of the body that causes
animal heat. It is a process similar to that which takes place when
lamps and candles are burning. The oil and tallows which are chiefly
carbon and hydrogen, unite with the oxygen of the air and form carbonic
acid and watery vapor, producing heat during the process. So in the
capillaries all over the body, the carbon and hydrogen supplied to the
blood by the stomach, unite with the oxygen gained in the lungs, and
cause the heat which is diffused all over the body.

The skin also performs an office, similar to that of the lungs. In the
skin of every adult there are no less than seven million minute
perspirating tubes, each one fourth of an inch long. If all these were
united in one length, they would extend twenty-eight miles. These
minute tubes are lined with capillary blood-vessels, which are
constantly sending out not only carbonic acid, but other gases and
particles of decayed matter. The skin and lungs together, in one day
and night, throw out three quarters of a pound of charcoal as carbonic
acid, beside other gases and water.

While the bodies of men and animals are filling the air with the
poisonous carbonic acid, and using up the life-giving oxygen, the trees
and plants are performing an exactly contrary process; for they are
absorbing carbonic acid and giving out oxygen. Thus, by a wonderful
arrangement of the beneficent Creator, a constant equilibrium is
preserved. What animals use is provided by vegetables, and what