njury which is continually done to
the atmosphere by the respiration of such a number of animals, and the
putrefaction of such masses of both vegetable and animal matter, is, in
part at least, repaired by the vegetable creation. And, notwithstanding
the prodigious mass of air that is corrupted daily by the
above-mentioned causes; yet, if we consider the immense profusion of
vegetables upon the face of the earth, growing in places, suited to
their nature, and consequently at full liberty to exert all their
powers, both inhaling and exhaling, it can hardly be thought, but that
it may be a sufficient counterbalance to it, and that the remedy is
adequate to the evil.

Dr. Franklin, who, as I have already observed, saw some of my plants in
a very flourishing state, in highly noxious air, was pleased to express
very great satisfaction with the result of the experiments. In his
answer to the letter in which I informed him of it, he says,

"That the vegetable creation should restore the air which is spoiled by
the animal part of it, looks like a rational system, and seems to be of
a piece with the rest. Thus fire purifies water all the world over. It
purifies it by distillation, when it raises it in vapours, and lets it
fall in rain; and farther still by filtration, when, keeping it fluid,
it suffers that rain to percolate the earth. We knew before that putrid
animal substances were converted into sweet vegetables, when mixed with
the earth, and applied as manure; and now, it seems, that the same
putrid substances, mixed with the air, have a similar effect. The strong
thriving state of your mint in putrid air seems to shew that the air is
mended by taking something from it, and not by adding to it." He adds,
"I hope this will give some check to the rage of destroying trees that
grow near houses, which has accompanied our late improvements in
gardening, from an opinion of their being unwholesome. I am certain,
from long observation, that there is nothing unhealthy in the air of
woods; for we Americans have every where our country habitations in the
midst of woods, and no people on earth enjoy better health, or are more
prolific."

Having rendered inflammable air perfectly innoxious by continued
_agitation in a trough of water_, deprived of its air, I concluded that
other kinds of noxious air might be restored by the same means; and I
presently found that this was the case with putrid air, even of more
than a year's standing.