become modified. There is a sense in
which it is true--and the analogy was pointed out very many years ago by
some French botanists and chemists--there is a sense in which it is
true that every plant is substantially an enormous aggregation of
bodies similar to yeast cells, each having to a certain extent its own
independent life. And there is a sense in which it is also perfectly
true--although it would be impossible for me to give the statement
to you with proper qualifications and limitations on an occasion like
this--but there is also a sense in which it is true that every animal
body is made up of an aggregation of minute particles of protoplasm,
comparable each of them to the individual separate yeast plant. And
those who are acquainted with the history of the wonderful revolution
which has been worked in our whole conception of these matters in the
last thirty years, will bear me out in saying that the first germ of
them, to a very great extent, was made to grow and fructify by the study
of the yeast plant, which presents us with living matter in almost its
simplest condition.

Then there is yet one last and most important bearing of this yeast
question. There is one direction probably in which the effects of the
careful study of the nature of fermentation will yield results more
practically valuable to mankind than any other. Let me recall to your
minds the fact which I stated at the beginning of this lecture. Suppose
that I had here a solution of pure sugar with a little mineral matter
in it; and suppose it were possible for me to take upon the point of a
needle one single, solitary yeast cell, measuring no more perhaps than
the three-thousandth of an inch in diameter--not bigger than one of
those little coloured specks of matter in my own blood at this moment,
the weight of which it would be difficult to express in the fraction
of a grain--and put it into this solution. From that single one, if the
solution were kept at a fair temperature in a warm summer's day, there
would be generated, in the course of a week, enough torulae to form
a scum at the top and to form lees at the bottom, and to change the
perfectly tasteless and entirely harmless fluid, syrup, into a solution
impregnated with the poisonous gas carbonic acid, impregnated with the
poisonous substance alcohol; and that, in virtue of the changes worked
upon the sugar by the vital activity of these infinitesimally small
plants. Now you see that this is