hat I know of, to the prodigious antiquity of the earth
since it existed in a condition in the main similar to that in which it
now is.

End of Coral and Coral Reefs.

YEAST.

I have selected to-night the particular subject of Yeast for two
reasons--or, rather, I should say for three. In the first place, because
it is one of the simplest and the most familiar objects with which we
are acquainted. In the second place, because the facts and phenomena
which I have to describe are so simple that it is possible to put them
before you without the help of any of those pictures or diagrams which
are needed when matters are more complicated, and which, if I had to
refer to them here, would involve the necessity of my turning away from
you now and then, and thereby increasing very largely my difficulty
(already sufficiently great) in making myself heard. And thirdly, I have
chosen this subject because I know of no familiar substance forming part
of our every-day knowledge and experience, the examination of which,
with a little care, tends to open up such very considerable issues as
does this substance--yeast.

In the first place, I should like to call your attention to a fact with
which the whole of you are, to begin with, perfectly acquainted, I mean
the fact that any liquid containing sugar, any liquid which is formed by
pressing out the succulent parts of the fruits of plants, or a mixture
of honey and water, if left to itself for a short time, begins to
undergo a peculiar change. No matter how clear it might be at starting,
yet after a few hours, or at most a few days, if the temperature is
high, this liquid begins to be turbid, and by-and-by bubbles make their
appearance in it, and a sort of dirty-looking yellowish foam or scum
collects at the surface; while at the same time, by degrees, a similar
kind of matter, which we call the "lees," sinks to the bottom.

The quantity of this dirty-looking stuff, that we call the scum and the
lees, goes on increasing until it reaches a certain amount, and then
it stops; and by the time it stops, you find the liquid in which this
matter has been formed has become altered in its quality. To begin with
it was a mere sweetish substance, having the flavour of whatever might
be the plant from which it was expressed, or having merely the taste and
the absence of smell of a solution of sugar; but by the time that this
change that I have been briefly describing to you is accomp