at one nerve fibre differed from another in the very essence of
its work. It was just about the end of the eighteenth century, or the
beginning of the nineteenth, that an English surgeon began to ponder over
a conception which, however, he did not make known until some years later,
and which did not gain complete demonstration and full acceptance until
still more years had passed away. It was in 1811, in a tiny pamphlet
published privately, that Charles Bell put forth his New Idea, that the
nervous system is constructed on the principle that "the nerves are not
single nerves possessing various powers, but bundles of different nerves,
whose filaments are united for the convenience of distribution, but which
are distinct in office, as they are in origin, from the brain."

Our present knowledge of the nervous system is to a large extent only an
exemplification and expansion of Charles Bell's New Idea, and has its
origin in that.

If we pass from the problems of the living organism viewed as a machine to
those presented by the varied features of the different creatures who have
lived or who still live on the earth, we at once call to mind that the
middle years of the nineteenth century mark an epoch in biologic thought
such as never came before; for it was then that Charles Darwin gave to the
world the "Origin of Species."

That work, however, with all the far-reaching effects which it has had,
could have had little or no effect, or, rather, could not have come into
existence, had not the earlier half of the century been in travail
preparing for its coming. For the germinal idea of Darwin appeals, as to
witnesses, to the results of two lines of biologic investigation which
were almost unknown to the men of the eighteenth century.

To one of these lines I have already referred. Darwin, as we know,
appealed to the geological record; and we also know how that record,
imperfect as it was then, and imperfect as it must always remain, has
since his time yielded the most striking proofs of at least one part of
his general conception. In 1799 there was, as we have seen, no geological
record at all.

Of the other line I must say a few words.

To-day the merest beginner in biologic study, or even that exemplar of
acquaintance without knowledge, the general reader, is aware that every
living being, even man himself, begins its independent existence as a tiny
ball, of which we can, even acknowledging to the full the limits of the