, on the other hand, by the Thenardian
doctrine, supported by Pasteur, according to which the yeast plant
assimilates part of the sugar, and, in so doing, disturbs the rest,
and determines its resolution into the products of fermentation.
Perhaps the two views are not so much opposed as they seem at first
sight to be.

But the interest which attaches to the influence of the yeast plants
upon the medium in which they live and grow does not arise solely
from its bearing upon the theory of fermentation. So long ago as 1838,
Turpin compared the _Torulae_ to the ultimate elements of the tissues
of animals and plants--"Les organes elementaires de leurs tissus,
comparables aux petits vegetaux des levures ordinaires, sont aussi les
decompositeurs des substances qui les environnent."

Almost at the same time, and, probably, equally guided by his study of
yeast, Schwann was engaged in those remarkable investigations into
the form and development of the ultimate structural elements of the
tissues of animals, which led him to recognize their fundamental
identity with the ultimate structural elements of vegetable organisms.

The yeast plant is a mere sac, or "cell," containing a semi-fluid
matter, and Schwann's microscopic analysis resolved all living
organisms, in the long run, into an aggregation of such sacs or cells,
variously modified; and tended to show, that all, whatever their
ultimate complication, begin their existence in the condition of such
simple cells.

In his famous "Mikroskopische Untersuchungen," Schwann speaks of
_Torula_ as a "cell;" and, in a remarkable note to the passage in
which he refers to the yeast plant, Schwann says:--

"I have been unable to avoid mentioning fermentation, because
it is the most fully and exactly known operation of cells,
and represents, in the simplest fashion, the process which is
repeated by every cell of the living body."

In other words, Schwann conceives that every cell of the living body
exerts an influence on the matter which surrounds and permeates it,
analogous to that which a _Torula_ exerts on the saccharine solution
by which it is bathed. A wonderfully suggestive thought, opening up
views of the nature of the chemical processes of the living body,
which have hardly yet received all the development of which they are
capable.

Kant defined the special peculiarity of the living body to be that the
parts exist for the sake of the whole and the whole fo