operations with a helping hand; animals and plants owe their lives to
it; but when the shadow of death begins to fall upon them, it is
as ready to aid in their destruction. Like calumny, which blackens
whatsoever is suspected, oxygen pounces upon the failing and completes
their ruin. The processes of fermentation and putrefaction cannot
commence in any substance, until it has first taken oxygen into
combination. Thus, cans of meat, hermetically sealed, with all the air
first carefully expelled, undergo no change so long as the air does not
get access to them. If the minutest opening remain, the oxygen of the
atmosphere combines with the contents of the can, and fermentation or
putrefaction follows. Rust, which takes the keen edge from the knife, is
only another name for oxydation: keep the knife bright, and no oxygen
dares touch it; but the slightest blemish is made a loophole for the
entrance of the ever-watchful enemy, who never again leaves it until its
destruction is complete.

All the elements have a great love of society; they cannot live alone;
they have their likes and their dislikes; they contract alliances which
endure for a time, but are dissolved in favor of stronger attractions.

We have mentioned the names of several natural elements. Let us see what
they are, and what they have to do with man and the kingdoms of Nature.
Beginning with man, let us see what becomes of him in course of time,
what physical metamorphoses he undergoes, to what vile but excellent
uses he is put.

That which forms the bone and muscle of a man this year may be upon his
own table in the shape of potatoes or peaches one summer later. When
Hamlet talked of turning the clay of Alexander into the bung of a
beer-barrel, he spoke the simple truth. In that great play, Shakspeare