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not sufficient ; it did not produce a sufficient amount of
enzyme to bring about this effect in blood, but when asso-
ciated in numbers the blood was decomposed sufficiently, the
plant was able to absorb material for its nutrition and grew
and multiplied. In this way these plants performed the act
of digestion in association, and then each cell takes from that
material the nutrition for itself and grows and multiplies.
And in this illustration (indicating) we find that the act of
digestion is performed by the enzyme passing through the
membrane, but the other functions of fermentation fail for
want of the presence of the organism. In this way the
enzyme of the plant is spread beyond the sphere of the plant.
The other functions must be performed by each individual
cell for itself—the acts of forming the waste products, car-
bonic acid and alcohol.
Now, similar studies to this have been made of micro-
organisms producing caries of the teeth. Miller, in his ex-
perimental work, obtained the enzyme of the plant and tried
its action upon cane sugar and upon starch, and found that
this is also a diastase that converts cane sugar into glucose
very readily. We have watched the growth of the plant
and found that it multiplies—reproduces similar forms—as
the yeast plant and as the higher animals do. It also forms
its waste product, which in this case is lactic acid instead of
alcohol and carbonic acid ; no gas is formed. Formerly it
was supposed that some gaseous product must be given off
from every plant, from every animal, but more recently it
has been well determined that there are many of the micro-
organisms that give off no gaseous waste product whatever.
So far as we yet know distinctly, the lactic acid is the only
waste product of certain micro-organisms of the mouth, and
yet we are not certain that there is not another waste prod-
uct of some other form. From some effects noted we have
reason to think there is. This whole matter, you must re-
member, is young; it has only been developing a few years;
in fact, the actual knowledge of it is not more than twenty
years old. For the studies were rude and imperfect before
Koch's discovery of planting upon solid media and the sepa-
ration of species in this way, and of staining methods by
which we could recognize micro-organisms more perfectly
by microscopic observation.

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