un's rays is qualified by the atoms and
molecules among which their energy is distributed. Molecular forces
determine the form which the solar energy will assume. In the
separation of the carbon and oxygen this energy may be so conditioned
as to result in one case in the formation of a cabbage, and in another
case in the formation of an oak. So also, as regards the reunion of
the carbon and the oxygen, the molecular machinery through which the
combining energy acts may, in one case, weave the texture of a frog,
while in another it may weave the texture of a man.

The matter of the animal body is that of inorganic nature. There is
no substance in the animal tissues which is not primarily derived from
the rocks, the water, and the air. Are the forces of organic matter,
then, different in kind from those of inorganic matter? The
philosophy of the present day negatives the question. It is the
compounding, in the organic world, of forces belonging equally to the
inorganic, that constitutes the mystery and the miracle of vitality.
Every portion of every animal body may be reduced to purely inorganic
matter. A perfect reversal of this process of reduction would carry
us from the inorganic to the organic; and such a reversal is at least
conceivable. The tendency, indeed, of modern science is to break down
the wall of partition between organic and inorganic, and to reduce
both to the operation of forces which are the same in kind, but which
are differently compounded.

Consider the question of personal identity, in relation to that of
molecular form. Thirty-four years ago, Mayer of Heilbronn, with that
power of genius which breathes large meanings into scanty facts,
pointed out that the blood was 6 the oil of the lamp of life,' the
combustion of which sustains muscular action. The muscles are the
machinery by which the dynamic power of the blood is brought into
play. Thus the blood is consumed. But the whole body, though more
slowly than the blood, wastes also, so that after a certain number of
years it is entirely renewed. How is the sense of personal identity
maintained across this flight of molecules? To man, as we know him,
matter is necessary to consciousness; but the matter of any period may
be all changed, while consciousness exhibits no solution of
continuity. Like changing sentinels, the oxygen, hydrogen, and carbon
that depart, seem to whisper their secret to their comrades that
arrive, and thus, whil