e we know? Or, is the
matter of life composed of ordinary matter, differing from it only in
the manner in which its atoms are aggregated? Is it built up of ordinary
matter, and again resolved into ordinary matter when its work is done?

Modern science does not hesitate a moment between these alternatives.
Physiology writes, over the portals of life--

"Debemur morti nos nostraque,"

with a profounder meaning than the Roman poet attached to that
melancholy line. Under whatever disguise it takes refuge, whether fungus
or oak; worm or man, the living protoplasm not only ultimately dies and
is resolved into its mineral and lifeless constituents, but is always
dying, and, strange as the paradox may sound, could not live unless it
died.

In the wonderful story of the "Peau de Chagrin," the hero becomes
possessed of a magical wild ass' skin, which yields him the means of
gratifying all his wishes. But its surface represents the duration of
the proprietor's life; and for every satisfied desire the skin shrinks
in proportion to the intensity of fruition, until at length life and the
last hand-breadth of the _peau de chagrin_, disappear with the
gratification of a last wish.

Balzac's studies had led him over a wide range of thought and
speculation, and his shadowing forth of physiological truth in this
strange story may have been intentional. At any rate, the matter of life
is a veritable _peau de chagrin_, and for every vital act it is somewhat
the smaller. All work implies waste, and the work of life results,
directly or indirectly, in the waste of protoplasm.

Every word uttered by a speaker costs him some physical loss; and, in
the strictest sense, he burns that others may have light--so much
eloquence, so much of his body resolved into carbonic acid, water, and
urea. It is clear that this process of expenditure cannot go on for
ever. But, happily, the protoplasmic _peau de chagrin_ differs from
Balzac's in its capacity of being repaired, and brought back to its full
size, after every exertion.

For example, this present lecture, whatever its intellectual worth to
you, has a certain physical value to me, which is, conceivably,
expressible by the number of grains of protoplasm and other bodily
substance wasted in maintaining my vital processes during its delivery.
My _peau de chagrin_ will be distinctly smaller at the end of the
discourse than it was at the beginning. By and by, I shall probably have
recourse to