probable the unbroken
sequence of development from the nebula to the present time.' Thus it
appears that, long antecedent to the publication of his advice, I did
exactly what Professor Virchow recommends, showing myself as careful
as he could be not to claim for a scientific doctrine a certainty
which did not belong to it.

I now pass on to the Belfast Address, and will cite at once from it
the passage which has given rise to the most violent animadversion.
'Believing as I do in the continuity of nature, I cannot stop abruptly
where our microscopes cease to be of use. At this point the vision of
the mind authoritatively supplements that of the eye. By an
intellectual necessity I cross the boundary of the experimental
evidence, and discern in that "matter" which we, in our ignorance of
its latent powers, and notwithstanding our professed reverence for its
Creator, have hitherto covered with opprobrium, the promise and
potency of all terrestrial life.' Without halting for a moment I go on
to do the precise thing which Professor Virchow declares to be
necessary. 'If you ask me,' I say, 'whether there exists the least
evidence to prove that any form of life can be developed out of matter
independently of antecedent life, my reply is that evidence considered
perfectly conclusive by many has been adduced, and that were we to
follow a common example, and accept testimony because it falls in with
our belief, we should eagerly close with the evidence referred to. But
there is in the true man of science a desire stronger than the wish to
have his beliefs upheld; namely, the desire to have them true. And
those to whom I refer as having studied this question, believing the
evidence offered in favour of "spontaneous generation" to be vitiated
by error, cannot accept it. They know full well that the chemist now
prepares from inorganic matter a vast array of substances, which were
some time ago regarded as the products solely of vitality. They are
intimately acquainted with the structural power of matter, as
evidenced in the phenomena of crystallisation. They can justify
scientifically their _belief_ in its potency, under the proper
conditions, to produce organisms. But, in reply to your question,
they will frankly admit their inability to point to any satisfactory
experimental proof that life can be developed, save from demonstrable
antecedent life.' [Footnote: Quoted by Clifford, 'Nineteenth Century,'
3, p. 726.]

Comparing