The hill-sides of the southern part of France are covered with
vineyards, where the luscious grapes round out under the late summer
sunshine into globes of delicious sweetness. When the grapes are ripe,
the peasants--men, women, and children--may be seen gayly trooping to
the vineyards to pick them for wine. In the famous Steinburger vineyard
the pickers are all girls about eighteen years old. Each girl has a row
to pick, and they begin together, and move forward as steadily and
evenly as a regiment of soldiers. With their gay petticoats looped up so
that they may not brush off the ripe grapes, and their bright stockings
and mittens, they make a very pretty picture moving along between the
rows, snipping the ripe grapes, and letting them drop into their
baskets. When the baskets are full they are emptied into a tub, which
the men lift by leathern straps and carry to the road-side press. The
juice which comes spurting out of the press is placed in vats or
barrels, and there left to ferment, which changes the juice, or _must_,
into wine. When the cook wants her bread to ferment, or rise, she plants
it with yeast; but the wine has nothing planted in it, and yet it
ferments.
Pasteur, the great French chemist, made up his mind to find why this
was. He was convinced from all his studies in fermentation that the
reason would be found in some little plant which was growing in the
juice and helping itself to whatever it needed to eat or to breathe. He
set to work to find out where the plants came from which turned the
grape juice into wine. All his experiments are so fully and clearly
explained that any one who is willing to take the pains can try them for
himself.
[Illustration: FIG. 1.--GRAPE FUNGUS.]
He found that there was no fungus growing inside the little closed bag
(which we call skin) in which the pulp, seed, and juice of the grape is
sealed up. There is no opening anywhere in a sound grape through which
spores (which are the fungus seed) could enter. But he found on the skin
of the grape, and thickly over the stem, little plants, something like
yeast and something like mould; these make up, in part, what is called
the bloom of the grape. He put some water, with these plants mixed
through it, into one tightly sealed bottle, and into another he put the
pure juice of the grapes which had none of the little plants through it,
and then waited to see what would happen. In a few days the water was
all yeasty, and the grape juice was unchanged. (Fig. 1.) He tried this
same thing over, and over, and over again, and in various ways, to be
sure that he was right. He thus found that the little magician that
turns the juice into wine is always waiting at the door of the sealed
chamber, ready to work its miracle as soon as it can reach the juice.
It is very different with beer. Pasteur gave a great deal of time and
attention to finding out why so many millions of gallons of beer were
every year spoiled in the making. The brewers could not tell why. They
prepared their wort in just the same way, and planted just the same
amount of yeast into the good beer as they did in what turned out to be
bad. He brought that wonderful microscope of his to bear upon the
subject. He found that whenever the wort was planted with yeast which
had certain curious little glassy rods mixed through it, the beer turned
sour. The brewer, when he put such yeast as this into his wort, was
planting, along with the seeds of the yeast plant, seeds of a
troublesome weed. The sour beer was really only a very queer kind of a
liquid garden, growing more weeds than useful plants.
[Illustration: FIG. 2.--POTATO FUNGUS.]
Vinegar is another thing made by these little fairy fungi. The cider out
of which it is made is set away in a cask to ferment. The spores that
work the change in this case are floating in the air, and manage somehow
to get into the open cask. Did you never notice the flakes of
muddy-looking substance at the bottom of a vinegar cruet? That is the
_mother_, the little plant that has made the cider into vinegar.
[Illustration: FIG. 3.--LEAF MILDEW.]
These are some of the useful things that are done by the fungi, and they
are certainly very valuable services. We owe to them our bread, and
wine, and beer, and vinegar. But they are not always benevolent fairies
by any means. Sometimes we are inclined to think that they are at the
bottom of pretty much all the mischief in the world. If they were not
sailing about in every breath of wind, getting into all sorts of places
where they are not wanted, we probably would never have any chills and
fever or diphtheria, and the yellow fever would not sweep off its
thousands and tens of thousands. If these little floating spores did not
get into every crack and cranny, wounds would not fester, damp linen
would not mildew, preserves and pickles would not mould, milk would not
sour, nothing would spoil or ferment or decay. There is an old proverb
that "the mother of mischief is no bigger than a midge's wing." I
sometimes wonder if the old-time people that made the proverbs did not
know something of these tiny mischiefs that only seem to be waiting the
chance to work their naughty will.
There is one case where this change takes place which you have probably
often seen. When I was a child I used to be very fond of getting from
the woods close to the house, or from the wood-pile, bits of shining
wood and bark, which we called "fox fire." The wood was always old and
decaying, and we thought it was shining because it was dying. But really
the perishing wood was covered all over with tiny mushrooms, which shone
with a light something like the glimmer of a fire-fly. In some countries
this brightness is very wonderful. In Australia people have been able to
read by the light of a shining stump overgrown with luminous fungi.
[Illustration: FIG. 4.--RYE SMUT.]
Some of the fungi have not even the manners to wait until their victims
are dead. They take possession of living plants and animals, and never
rest until they have destroyed them. The disease among potatoes called
the potato blight (Fig. 2), of which we hear so much, is caused by the
growth of a little fungous plant in the mouths, or breathing holes, on
the skin of the potato, and the blight and mildew (Fig. 3) and smut of
wheat and corn and rye (Fig. 4) are all due to the same cause. The
mouldy look upon vine leaves is nothing else. I put a leaf of Virginia
creeper which looked whitish and ugly under the microscope one day, and
found the whole surface covered with a net-work of silvery threads, with
a wonderful, fruit growing upon it. The fruits looked like peeled
oranges surrounded with threads of spun sugar, or occasionally like a
gigantic blackberry sparkling with crystals. This was only a common
mildew, but under the magnifier it seemed a wonderful garden, growing
conserves and fairy fruits, and was beautiful, beyond description. (Fig.
5.)
[Illustration: FIG. 5.--MILDEW ON VIRGINIA CREEPER.]
The silk-worm is attacked by a fungous plant (Fig. 6). It takes
possession of the worm just before it begins to spin its cocoon, and
some years ago it destroyed such multitudes that the French silk trade
was seriously threatened. The microscope was again brought into use, and
the cause of the trouble discovered, and the cure effected.
[Illustration: FIG. 6.--SILK-WORM FUNGUS.]
The untiring Pasteur studied up this and other diseases of the silk-worm
as he did those of wine and beer, and helped the silk-worm growers to
stamp out the disease when it appeared. It perhaps seems a small thing
for a man of genius like Pasteur to give his whole life to studying
these little plants through the microscope, but never was a life more
helpfully and patriotically spent. Hundreds of thousands of the French
peasants depended for daily food and shelter upon what they earned in
the wine and beer and silk trades, and these trades Pasteur's work has
saved from destruction or great loss. It has been said that his work
with the microscope has saved to France more than the awful French
Revolution cost her.