e rays of the sun, is
conveyed even into the composition of man himself. As food, they serve
to repair the waste of the body necessarily occasioned in the acts of
moving and thinking. For a time, therefore, these ingredients, once a
part of the structure of plants, enter as essential constituents in the
structure of animals. Yet it is only in a momentary way, for the
essential condition of animal activity is that there shall be unceasing
interstitial death; not a finger can be lifted without the waste of
muscular material; not a thought arise without the destruction of
cerebral substance. From the animal system the products of decay are
forthwith removed, often by mechanisms of the most exquisite
construction; but their uses are not ended, for sooner or later they
find their way back again into the air, and again serve for the
origination of plants. It is needless to trace these changes in all
their details; the same order or cycle of progress holds good for the
water, the ammonia; they pass from the inorganic to the living state,
and back to the inorganic again; now the same particle is found in the
air next aiding in the composition of a plant, then in the body of an
animal, and back in the air once more. In this perpetual revolution
material particles run, the dominating influence determining and
controlling their movement being in that great centre of our system, the
sun. From him, in the summer days, plants receive, and, as it were,
store up that warmth which, at a subsequent time, is to reappear in the
glow of health of man, or to be rekindled in the blush of shame, or to
consume in the burning fever. Nor is there any limit of time. The heat
we derive from the combustion of stubble came from the sun as it were
only yesterday; but that with which we moderate the rigour of winter
when we burn anthracite or bituminous coal was also derived from the
same source in the ultra-tropical climate of the secondary times,
perhaps a thousand centuries ago.

In such perpetually recurring cycles are the movements of material
things accomplished, and all takes place under the dominion of
invariable law. The air is the source whence all organisms have come; it
is the receptacle to which they all return. Its parts are awakened into
life, not by the influence of any terrestrial agency or principle
concealed in itself, as Diogenes supposed, but by a star which is ninety
millions of miles distant, the source, direct or indirect, of ev