VITALITY. 379 
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 compound- 
ing, 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 
" 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, while the 
Non-ego shifts, the Ego remains the same. Constancy of 
form in the grouping of the molecules, and not constancy 
of the molecules themselves, is the correlative of this con- 
stancy of perception. Life is a wave which in no two 
consecutive moments of its existence is composed of the 
same particles. 
Supposing, then the molecules of the human body, 
