Biology | Page 3

that a Newton may one day arise who will make the production
of a blade of grass comprehensible to us according to natural laws that
have not been ordered by design. Such an insight we must absolutely
deny to man." Still, 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, life, as
thus viewed, seems to have its root in chemical change; and we can
understand how an eminent German physiologist offers us a definition
or characterization of life that runs: "The life-process consists in the
metabolism of proteids." I ask your particular attention to this
definition since I now wish to contrast with it another and very
different one.
I shall introduce it to your attention by asking a very simple question.
We may admit that digestion, for example, is a purely chemical
operation, and one that may be exactly imitated outside the living body
in a glass flask. My question is, how does it come to pass that an
animal has a stomach?--and, pursuing the inquiry, how does it happen
that the human stomach is practically incapable of digesting cellulose,
while the stomachs of some lower animals, such as the goat, readily
digest this substance? The earlier naturalists, such as Linnaeus, Cuvier
or Agassiz, were ready with a reply which seemed so simple, adequate
and final that the plodding modern naturalist cannot repress a feeling of
envy. In their view plants and animals are made as they were originally
created, each according to its kind. The biologist of to-day views the
matter differently; and I shall give his answer in the form in which I
now and then make it to a student who may chance to ask why an
insect has six legs and a spider eight, or why a yellowbird is yellow and
a bluebird blue. The answer is: "For the same reason that the elephant
has a trunk." I trust that a certain rugged pedagogical virtue in this reply
may atone for its lack of elegance. The elephant has a trunk, as the

insect has six legs, for the reason that such is the specific nature of the
animal; and we may assert with a degree of probability that amounts to
practical certainty that this specific nature is the outcome of a definite
evolutionary process, the nature and causes