are very near to every-day truths. We must begin with some plain
statements.

The air which we expel from the lungs at every breath has a large
proportion of carbonic acid. Let a man be shut up in an air-tight room
for a day, and he will have changed nearly all the oxygen in it into
this carbonic acid, and rendered it unfit for animal life. Dogs, cats,
and birds would die in it. But, poisonous as it is to man and other
animals, it is a feast to plants. They want it all day and every day;
not in the night,--at that time they have a taste for oxygen. This
effete air, which men and animals exhale, so charged with carbonic acid,
the plants drink in through every pore. They take it from the mouth of
man, appropriate it to their daily uses, and in time render it back to
him mingled with other ingredients in wholesome fruit. Carbonic acid is
death when it combines with the blood,--as it does when we inhale
it; but not so when it enters the stomach in small quantities. One
inspiration of it is enough to make us dizzy,--as when we enter an old
well or stoop over a charcoal fire; but a draught of water fully
charged with it is exhilarating and refreshing, as we know by repeated
experiences at marble fountains that meet us on so many city-corners.

If plants had souls, they would be pure ones, since they can bear such
contamination and not be harmed,--nay, since even from such foul food
as we give them they can evolve results so beautiful. We give them our
cast-off and worn-out materials, and they return us the most beautiful
flowers and the most luscious fruits.

Beside carbonic acid, there are two other principal materials, which
are every day passing off in an effete state, though capable of being
transferred to the uses of plants. But when an animal dies, the whole