ongly, I must
carefully guard myself against the supposition that I intend to suggest
that no such thing as Abiogenesis ever has taken place in the past, or
ever will take place in the future. With organic chemistry, molecular
physics, and physiology yet in their infancy, and every day making
prodigious strides, I think it would be the height of presumption for any
man to say that the conditions under which matter assumes the properties
we call "vital" may not, some day, be artificially brought together. All
I feel justified in affirming is, that I see no reason for believing that
the feat has been performed yet.

And looking back through the prodigious vista of the past, I find no
record of the commencement of life, and therefore I am devoid of any
means of forming a definite conclusion as to the conditions of its
appearance. Belief, in the scientific sense of the word, is a serious
matter, and needs strong foundations. To say, therefore, in the admitted
absence of evidence, that I have any belief as to the mode in which the
existing forms of life have originated, would be using words in a wrong
sense. But expectation is permissible where belief is not; and if it were
given me to look beyond the abyss of geologically recorded time to the
still more remote period when the earth was passing through physical and
chemical conditions, which it can no more see again than a man can recall
his infancy, I should expect to be a witness of the evolution of living
protoplasm from not living matter. I should expect to see it appear under
forms of great simplicity, endowed, like existing fungi, with the power
of determining the formation of new protoplasm from such matters as
ammonium carbonates, oxalates and tartrates, alkaline and earthy
phosphates, and water, without the aid of light. That is the expectation
to which analogical reasoning leads me; but I beg you once more to
recollect that I have no right to call my opinion anything but an act of
philosophical faith.

So much for the history of the progress of Redi's great doctrine of
Biogenesis, which appears to me, with the limitations I have expressed,
to be victorious along the whole line at the present day.

As regards the second problem offered to us by Redi, whether Xenogenesis
obtains, side by side with Homogenesis,--whether, that is, there exist
not only the ordinary living things, giving rise to offspring which run
through the same cycle as themselves, but also others,