l, in another
place Kant admitted that the facts of comparative anatomy give us "a
ray of hope, however faint, that something may be accomplished by the
aid of the principle of the mechanism of nature, without which there
can be no science in general." It is interesting to turn from this to
the bold and aggressive assertion of Huxley: "Living matter differs
from other matter in degree and not in kind, the microcosm repeats the
macrocosm; and one chain of causation connects the nebulous origin of
suns and planetary systems with the protoplasmic foundations of life
and organization."

Do not expect me to decide where such learned doctors disagree; but I
will at this point venture on one comment which may sound the key-note
of this address. Perhaps we shall find that in the long run and in the
large sense Kant was right; but it is certain that to-day we know
very much more about the formation of the living body, whether a blade
of grass or a man, than did the naturalists of Kant's time; and for
better or for worse the human mind seems to be so constituted that it
will continue its efforts to explain such matters, however difficult
they may seem to be. But I return to our more specific inquiry with
the remark that the history of physiology in the past two hundred
years has been the history of a progressive restriction of the notion
of a "vital force" or "vital principle" within narrower and narrower
limits, until at present it may seem to many physiologists that no
room for it remains within the limits of our biological philosophy.
One after another the vital activities have been shown to be in
greater or less degree explicable or comprehensible considered as
physico-chemical operations of various degrees of complexity. Every
physiologist will maintain that we cannot name one of these
activities, not even thought, that is not carried on by a physical
mechanism. He will maintain further that in most cases the vital
actions are not merely accompanied by physico-chemical operations but
actually consist of them; and he may go so far as definitely to
maintain that we have no evidence that life itself can be regarded as
anything more than their sum total. He is able to bring forward cogent
evidence that all modes of vital activity are carried on by means of
energy that is set free in protoplasm or its products by means of
definite chemical processes collectively known as metabolism. When the
matter is reduced to its lowest terms