"Verum talis mihi de horum origine et formatione conceptus formabam;
globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se
constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam
cerevisiam vocare licet, refrigescente, multos ex minimis particulis in
cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae
sexta pars est globuli faecis, et iterum sex ex hisce globulis
conjungi."[3]

[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.]

Thus Leeuwenhoek discovered that yeast consists of globules floating in a
fluid; but he thought that they were merely the starchy particles of the
grain from which the wort was made, rearranged. 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 Kützing 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