late, and found that with the destruction of
the organism, though its chemical constituents remained, the power to
act as a ferment totally disappeared.

One word more in reference to Liebig may find a place here. To the
philosophic chemist thoughtfully pondering these phenomena, familiar
with the conception of molecular motion, and the changes produced by
the interactions of purely chemical forces, nothing could be more
natural than to see in the process of fermentation a simple
illustration of molecular instability, the ferment propagating to
surrounding molecular groups the overthrow of its own tottering
combinations. Broadly considered, indeed, there is a certain amount
of truth in this theory; but Liebig, who propounded it, missed the
very kernel of the phenomena when he overlooked or contemned the part
played in fermentation by microscopic life. He looked at the matter
too little with the eye of the body, and too much with the spiritual
eye. He practically neglected the microscope, and was unmoved by the
knowledge which its revelations would have poured in upon his mind.
His hypothesis, as I have said, was natural--nay it was a striking
illustration of Liebig's power to penetrate and unveil molecular
actions; but it was an error, and as such has proved an ignis fatuus
instead of a pharos to some of his followers.

*****

I have said that our air is full of the germs of ferments differing
from the alcoholic leaven, and sometimes seriously interfering with
the latter. They are the weeds of this microscopic garden which often
overshadow and choke the flowers. Let us take an illustrative case.
Expose milk to the air. It will, after a time, turn sour, separating
like blood into clot and serum. Place a drop of this sour milk under
a powerful microscope and watch it closely. You see the minute
butter-globules animated by that curious quivering motion called the
Brownian motion. But let not this attract your attention too much,
for it is another motion that we have now to seek. Here and there you
observe a greater disturbance than ordinary among the globules; keep
your eye upon the place of tumult, and you will probably see emerging
from it a long eel-like organism, tossing the globules aside and
wriggling more or less rapidly across the field of the microscope.
Familiar with one sample of this organism, which from its motions
receives the name of vibrio, you soon detect numbers of them. It is
these organi