had the
same sort of relation to the thing itself as a man's spirit is supposed
to have to his body; and so they spoke of this fine essence of the
fermented liquid as being the spirit of the liquid. Thus came about
that extraordinary ambiguity of language, in virtue of which you apply
precisely the same substantive name to the soul of man and to a glass
of gin! And then there is still yet one other most curious piece of
nomenclature connected with this matter, and that is the word "alcohol"
itself, which is now so familiar to everybody. Alcohol originally meant
a very fine powder. The women of the Arabs and other Eastern people are
in the habit of tingeing their eyelashes with a very fine black powder
which is made of antimony, and they call that "kohol;" and the "al" is
simply the article put in front of it, so as to say "the kohol." And
up to the 17th century in this country the word alcohol was employed to
signify any very fine powder; you find it in Robert Boyle's works that
he uses "alcohol" for a very fine subtle powder. But then this name of
anything very fine and very subtle came to be specially connected with
the fine and subtle spirit obtained from the fermentation of sugar; and
I believe that the first person who fairly fixed it as the proper name
of what we now commonly call spirits of wine, was the great French
chemist Lavoisier, so comparatively recent is the use of the word
alcohol in this specialised sense.

So much by way of general introduction to the subject on which I have to
speak to-night. What I have hitherto stated is simply what we may call
common knowledge, which everybody may acquaint himself with. And
you know that what we call scientific knowledge is not any kind
of conjuration, as people sometimes suppose, but it is simply the
application of the same principles of common sense that we apply to
common knowledge, carried out, if I may so speak, to knowledge which is
uncommon. And all that we know now of this substance, yeast, and all the
very strange issues to which that knowledge has led us, have simply come
out of the inveterate habit, and a very fortunate habit for the human
race it is, which scientific men have of not being content until they
have routed out all the different chains and connections of apparently
simple phenomena, until they have taken them to pieces and understood
the conditions upon which they depend. I will try to point out to you
now what has happened in consequence of