ranged. He discovered
the fact that yeast had a definite structure, but not the meaning of
the fact. A century and a half elapsed, and the investigation of
yeast was recommenced almost simultaneously by Cagniard de la Tour in
France, and by Schwann and Kuetzing in Germany. The French observer
was the first to publish his results; and the subject received at his
hands and at those of his colleague, the botanist Turpin, full and
satisfactory investigation.

The main conclusions at which they arrived are these. The globular,
or oval, corpuscles which float so thickly in the yeast as to make it
muddy, though the largest are not more than one two-thousandth of
an inch in diameter, and the smallest may measure less than one
seven-thousandth of an inch, are living organisms. They multiply with
great rapidity, by giving off minute buds, which soon attain the size
of their parent, and then either become detached or remain united,
forming the compound globules of which Leeuwenhoek speaks, though the
constancy of their arrangement in sixes existed only in the worthy
Dutchman's imagination.

It was very soon made out that these yeast organisms, to which Turpin
gave the name of _Torula cerevisiae_, were more nearly allied to the
lower Fungi than to anything else. Indeed Turpin, and subsequently
Berkeley and Hoffmann, believed that they had traced the development
of the _Torula_ into the well-known and very common mould--the
_Penicillium glaucum_. Other observers have not succeeded in verifying
these statements; and my own observations lead me to believe, that
while the connection between _Torula_ and the moulds is a very close
one, it is of a different nature from that which has been supposed. I
have never been able to trace the development of _Torula_ into a true
mould; but it is quite easy to prove that species of true mould,
such as _Penicillium_, when sown in an appropriate nidus, such as
a solution of tartrate of ammonia and yeast-ash, in water, with or
without sugar, give rise to _Torulae_, similar in all respects to _T.
cerevisiae_, except that they are, on the average, smaller. Moreover,
Bail has observed the development of a _Torula_ larger than _T.
cerevisiae_, from a _Mucor_, a mould allied to _Penicillium_.

It follows, therefore, that the _Torulae_, or organisms of yeast,
are veritable plants; and conclusive experiments have proved that the
power which causes the rearrangement of the molecules of the sugar is
intima