question of spontaneous generation.' The Academy added that it demanded
precise and rigorous experiments equally well studied on all sides;
such experiments, in short, as should render it possible to deduce from
them results free from all confusion due to the experiments themselves.
Pasteur carried away the prize, and no one, it will be acknowledged,
deserved it better than he. Nevertheless, to his eyes, the subject was
still beset with difficulties. In the hot discussions to which the
question of spontaneous generation gave rise, the partisans of the
doctrine continually brought forward an objection based on an opinion
already referred to, and first enunciated by Gay-Lussac. As already
known to the reader, Gay-Lussac had arrived at the conclusion that,
in Appert's process, one condition of the preservation of animal and
vegetable substances consisted in the exclusion of oxygen.
Even this proposition was soon improved upon, and it became a current
opinion in science that the smallest bubble of oxygen or of air which
might come in contact with a preserve would be sufficient to start
its decomposition. The partisans of spontaneous generation--the
heterogenists--thenceforward threw their objections to Pasteur into
this form:
'How can the germs of microscopic organisms be so numerous that even
the smallest bubble of air contains germs capable of developing
themselves in every organic infusion? If such were the case the air
would be encumbered with organic germs.' M. Pouchet said and wrote that
they would form a thick fog, as dense as iron.
But Pasteur showed that the interpretation of Gay-Lussac's experiment,
with respect to the possible alteration of preserves by a small
quantity of oxygen gas, was quite erroneous. If, after a certain time,
an Appert preserve contains no oxygen, this is simply because the
oxygen has been gradually absorbed by the substances of the preserve,
which are always more or less chemically oxidisable. But in reality
it is easy to find oxygen in these preserves. Pasteur did not fail to
perceive that the interpretation given to Gay-Lussac's experiment was
wrong in another particular. He proved the fallacy of the assumption
that the smallest quantity of air was always capable of producing
microscopic organisms.
More thickly spread in towns than in the country, the germs become
fewer in proportion as they recede from human habitations. Mountains
have fewer than plains, and at a certain height they are very rare.
Pasteur's experiments to prove these facts were extremely simple. He
took a series of bulbs of about a quarter of a litre in capacity, and,
after having half filled the bulbs with a putrescible liquid, he drew
out the necks by means of the blowpipe, then he caused the liquid to
boil for some minutes, and during the ebullition, while the steam
issued from the tapering ends of the bulbs, he sealed them with the
lamp. Thus prepared, the bulbs can be easily transported. As they are
empty of air--that which they originally contained having been driven
out with the steam--when the sealed end of a bulb is broken off, the
air rushes into the tube, carrying with it all the germs which this
air holds in suspension. If it is closed again immediately afterwards
by a flame, and if the vessels are then left to themselves, it is easy
to recognise those in which a change occurs. Now, Pasteur established
that, in whatever place the operation might be carried on, a certain
number of bulbs would escape alteration. They must not, however, be
opened in a room after dusting the furniture or sweeping the floor, for
in this case all the bulbs would become altered because of the great
quantity of germs raised by the dusting and remaining suspended in the
air.
Pasteur started for Arbois with a series of bulbs. Some he opened in
the country far from all habitations; others he opened at the foot
of the mountains which form the first range of the Jura; a series of
twenty-four bulbs was opened upon Mount Poupet, at 850 meters above the
level of the sea; and, lastly, twenty others were transported to the
Montanvert, near the Mer de Glace, at an elevation of 2,000 meters.
He afterwards brought his whole collection back to Paris, and in the
month of November, 1860, deposited them on the table at the Academy of
Sciences.
Of the twenty bulbs first opened in the country, eight contained
organised productions. Of the twenty opened on the heights of the Jura,
five only were altered, and of the twenty opened upon the Montanvert
during a strong wind which blew from the glacier, one alone was altered.
If a similar series of experiments were made in a balloon, it would be
found that the air of the higher atmosphere is absolutely free from
germs. Care would, however, be necessary to prevent the introduction of
dust particles, which the rigging and the aëronauts themselves might
carry with them.
But we have not yet related all. So far, all these conclusive
experiments had been made only on organic liquids, very putrescible
it is true, but which had all been subjected to boiling or even to
temperatures higher than 100 degrees Centigrade. The partisans of
spontaneous generation might then be justified in saying that if the
precaution had been taken of putting into contact with pure air natural
organic liquids in a state compatible with the operations of animal
and vegetable life, the results would have been different. Under such
conditions, life would have appeared spontaneously in the production of
microscopic organisms. None of Pasteur's opponents had formulated this
argument; but Pasteur himself, who had within him an adversary always
present, always on the alert, prepared to yield only to accumulated
proofs, saw this objection. He was not satisfied until he had succeeded
in completely refuting it. Having by means of ingenious experimental
arrangements deprived some air of all living germs, he placed in
contact with this pure air the most putrescible liquids, particularly
venous blood, arterial blood, and urine. He took these liquids directly
from the veins, the arteries, and the bladders of animals in full
health. No alteration was produced. In due time a chemical absorption
of small quantities of oxygen took place, but neither fermentation nor
putrefaction, nor the smallest development of bacteria, of vibrios, or
of mould. After this, Pasteur was able legitimately to exclaim in his
celebrated lecture at the Sorbonne:
'There is not one circumstance known at the present day which
justifies the assertion that microscopic organisms come into the world
without germs or without parents like themselves. Those who maintain
the contrary have been the dupes of illusions and of ill-conducted
experiments, tainted with errors which they know not how either to
perceive or to avoid. Spontaneous generation is a chimera.'
Pasteur was not alone in affirming this fixed conviction. With the
authority of a judge delivering sentence in court, M. Flourens,
permanent Secretary of the Academy of Sciences, pronounced these words
before the whole Academy:
'As long as my opinion was not formed I had nothing to say; now
it _is_ formed and I can speak. The experiments are decisive. If
spontaneous generation be a fact, what is necessary for the production
of animalculæ? Air and putrescible liquids. Now Pasteur puts together
air and putrescible liquids and nothing is produced. Spontaneous
generation, then, has no existence. Those who still doubt have failed
to grasp the question.'
But some adversaries remained incredulous. When Pasteur had announced
the result of his experiments, and brought before the Academy his
series of bulbs, Pouchet and Joly declared that if Pasteur had opened
his bulbs in the Jura and on the Mer de Glace, they, on their part, had
been on the top of the Maladetta, and had proved there the inexactitude
of Pasteur's results.
Pasteur asked to be judged by the Academy. 'A commission alone,' said
he, 'will terminate the debate.' The commission was named, and the
position on both sides was clearly stated.
'I affirm,' said Pasteur, 'that everywhere it is possible to take
from the midst of the atmosphere a certain quantity of air which
contains neither egg nor spore, and which does not produce organisms in
putrescible solutions.'
On his side, M. Joly wrote: 'If one alone of your bulbs remains
unaltered we shall loyally acknowledge our defeat.' Lastly, M.
Pouchet, as distinct and positive as M. Pasteur, said: 'I affirm that
in whatever place I take a cubic decimeter of air, when this air
is placed in contact with a fermentable liquid enclosed in a glass
vessel hermetically sealed, the liquid will become filled with living
organisms.'
This double declaration, which excited at that time all the learned
world, took place in the month of January, 1864. Eager to engage in the
combat, Pasteur waited impatiently for the order of the Commission that
this experiment, which was to decide everything, should be made. But M.
Pouchet begged for a postponement, desiring, he said, to wait for the
warm season. Pasteur was astonished, but resigned himself to the delay.
The Commission and the opponents met on June 15.
The Commission announced, 'that, as the whole dispute turned upon one
simple fact, one single experiment ought to be undertaken, which alone
would close the discussion.'
The partisans of spontaneous generation wished nevertheless to go
through the entire series of their experiments. In vain the Commission
tried to persuade them that this would make the judgment as long as the
discussion itself had been, that all bore upon one fact, and that this
fact could be decided by a single experiment. The heterogenists would
not listen to this. M. Pouchet and M. Joly withdrew from the contest.
M. Jamin, an exact and authorised historian of these debates, observed
that 'the heterogenists, however they may have covered their retreat,
were thereby self-condemned. If they had been sure of the fact--which
they were solemnly engaged to prove, under penalty of acknowledging
themselves defeated--they would have hastened to demonstrate it, for
it would have been the triumph of their doctrine. People do not allow
themselves to be condemned by default except in causes in which they
have no confidence.'
_STUDIES ON WINE._
Having thus solved the problem of spontaneous generation, a problem
which was but a parenthesis forced upon his attention, Pasteur
returned to fermentation. Guided by his studies on vinegar and other
observations of detail, he undertook an inquiry into the diseases of
wine. The explanations of the changes which wine was known to undergo
rested only on hypothesis. From the time of Chaptal, who was followed
by Liebig and Berzelius, all the world believed wine to be a liquid
in which the various constituents react upon each other mutually
and slowly. The wine was thought to be continually 'working.' When
the fermentation of the grape is finished, equilibrium is not quite
established between the diverse elements of the liquor. Time is needed
for them to blend together. If this reciprocal action be not regular,
the wine becomes bad. This was, in other words, the doctrine of
spontaneity. Without support from carefully reasoned experiments, these
explanations could not satisfy Pasteur, especially at a moment when he
had just been proving that there was nothing spontaneous either in the
phenomena of fermentation or in animal and vegetable infusions.
Pasteur tried first of all to show that wine does not 'work' as
much as it was supposed to do. Wine being a mixture of different
substances, among which are acids and alcohol, particular ethers are
no doubt formed in it in course of time, and similar reactions perhaps
take place between the other constituents of the liquid. But if the
exactitude of such facts cannot be denied, based as they are upon
general laws, confirmed and extended by recent inquiries, Pasteur
thought that a false application was made of them when they were
employed to explain the maladies of wine, the changes which occur in
it through age--in a word, the alterations, whether good or bad, which
wines are subject to. The 'ageing' of wine soon appeared to him to
consist essentially in the phenomena of oxidation, due to the oxygen of
the air which dissolves and is diffused in the wine. He gave manifest
proofs of this. I will only mention one of them. New wine inclosed
in a glass vessel hermetically sealed keeps its freshness; it does
not 'work,' it does not 'age.' Pasteur demonstrated besides, that all
the processes of wine-making are explained by the double necessity
of oxygenising the wine to a suitable degree, and of preventing
its deterioration. In seeking for the actual causes of injurious
alterations, Pasteur, always obedient to a preconceived idea, while
carefully controlling it with the utmost rigour of the experimental
method, asked himself whether the diseases of wine did not proceed
from organised ferments, from little microscopic vegetations? In the
observed alterations, he thought, there must be some influences at work
foreign to the normal composition of the wine.
This hypothesis was verified. In his hands the injurious modifications
suffered by wines were shown to be correlative with the presence and
the multiplication of microscopic vegetations. Such growths alter
the wine, either by subtracting from it what they need for their
nourishment, or, and principally, by forming new products which are the
effect of the multiplication of these parasites in the mass of the wine.
Everyone knows what is meant by _acid wine_, _sharp wine_, _sour wine_.
The former experiments of Pasteur had clearly shown that no wine
can become acid, sharp--can, in a word, become vinegar--without the
presence of a little microscopic fungus known by the name of _mycoderma
aceti_. This little plant is the necessary agent in the condensation
of the oxygen of the air, and its fixation on the alcohol of the wine.
Chaptal, who published a volume on the art of wine-making, knew of the
existence of these mycoderm flowers; but to his eyes they were only
'elementary forms of vegetation,' which had no influence whatever upon
the quality of the liquid. Besides the _mycoderma aceti_, which is the
agent of acetification, there is another mycoderm called _mycoderma
vini_. This one deposits nothing which is hurtful to the wine, and its
flowers are developed by preference in new wines, still immature, and
preserving the astringency of the first period of their fabrication.
The requirements of the two sorts of flowers are such that even
when the flower of vinegar is sown on the surface of a new wine, no
development takes place. Conversely, the _mycoderma vini_ sown on wines
that have grown old in casks or in bottles will refuse to multiply. The
_mycoderma vini_ produces no alteration in the wine; it does not turn
the wine acid. In proportion as the wine grows old the flower tends to
disappear, the wine 'despoils' itself, to use a technical expression;
physiologically speaking, the wine loses its aptitude to nourish the
_mycoderma vini_, which, finding itself progressively deprived of
appropriate nourishment, fades and withers. But it is then that the
_mycoderma aceti_ appears, and multiplies with a facility so much the
greater that it draws its first nourishment from the cells of the
_mycoderma vini_. The _mycoderma aceti_ has played so large a part in
the early pages of this book that it is not necessary to go back upon
it here.
There is another disease very common among wines when the great heat
of summer begins to make itself felt in the vintage tubs. The wine
is said to _turn_, to _rise_, to _spurt_. The wine becomes slightly
turbid and at the same time flat and piquant. When it is poured into a
glass, very small bubbles of gas form like a crown upon the surface.
On placing the glass between the eye and the light and slightly
shaking it, one can distinguish silky waves shifting about and moving
in different directions in the liquid. When the _turned_ wine is in a
cask, it is not unusual to see the bottom of the cask bulge a little
and sometimes a leakage takes place at the joints of the staves. If a
little opening is made, the wine spurts out, and that is the reason why
the wine is said to spurt.
Authors who have written on the subject of wine attributed this malady
to the rising of the lees. They believed that the deposit which always
exists in greater or less quantities in the lower part of the cask
rises and spreads itself into all the mass of the wine.
Nothing can be more inexact. If this phenomenon is sometimes
produced--that is to say, if the deposit rises into the mass of
wine--the effect is due to a sudden diminution of the atmospheric
pressure, as in times of storm, for example. As the wine is always
charged with carbonic acid gas, which it holds in solution from the
moment of fermentation, one can conceive that a lowering of barometric
pressure would cause the escape of some bubbles of carbonic acid.
These bubbles, rising from the lower part of the cask, may disturb a
portion of the deposit, which then mixes with the wine and renders
it turbid. But the real cause of the disease is quite different. The
turbidity is without exception due to the presence of little filaments
of an extreme tenuity, about a thousandth part of a millimeter in
diameter. Their length is very variable. It is these which, when the
wine is agitated, give rise to the silky waves just referred to. Often
the deposit of the casks leaves a swarm of these filaments entangled
in each other, forming a glutinous mass, which under the microscope is
seen to be composed entirely of these little filaments. In acting upon
certain constituents of the wine particularly upon the tartar, this
ferment generates carbonic acid. The phenomenon of spurting is then
produced, because when the cask is closed the internal pressure of the
liquid augments. The sparkling and the crown of little gas-bubbles,
observed when the turned wine is poured out into a glass, is similarly
explained. In a word, the disease of turned wine is nothing else than
a fermentation, due to an organised ferment which, without any doubt,
proceeds originally from germs existing on the surface of the grapes
at the moment of gathering them, or on spoilt grapes such as are found
in every vintage. It is very rare not to find this parasite of turned
wine in the deposit of the wine at the bottom of the casks, but the
parasite is not troublesome unless it multiplies very largely. Pasteur
found the means of preventing this multiplication by a very simple
remedy, equally applicable to other diseases of wines, such as that of
bitterness or greasiness (_maladie de la graisse_).
Many wines acquire with age a more or less bitter taste, sometimes to
a degree which renders them unfit for consumption. Red wines, without
exception, are subject to this disease. It attacks by preference wines
of the best growth, and particularly the finest wines of the Côte-d'Or.
It is once more a little filamented fungus which works the change;
and not only does it cause in the wine a bitterness which little by
little deprives it of all its better qualities, but it forms in the
bottles a deposit which never adheres to the glass, but renders the
wine muddy or turbid. It is in this deposit that the filaments of
the fungus float. If white wines do not suffer from this disease of
bitterness, they are exposed, particularly the white wines of Orleans
and of the basin of the Loire, to the disease of greasiness. The wines
lose their limpidity; they become flat and insipid and viscous, like
oil when poured out. The disease declares itself in the casks or in the
best-corked bottles. M. Pasteur has discovered that the greasiness of
wines is likewise produced by a special ferment, which the microscope
shows to be formed of filaments, like the ferments of the preceding
diseases, but differing in structure from the other organisms, and in
their physiological action on the wine.
In short, according to Pasteur's observations, the deterioration of
wines should not in any case be attributed to a natural working of
the constituents of the wine, proceeding from a sort of interior
spontaneous movement, which would only be affected by variations
of temperature or atmospheric pressure. They are, on the contrary,
exclusively dependent on the development of microscopic organisms,
the germs of which exist in the wine from the moment of the original
fermentation which gave it birth. What vast multitudes of germs of
every kind must there not be introduced into every vintage tub! What
modifications do we not meet with in the leaves and in the fruit of
each individual spoilt vine! How numerous are the varieties of organic
dust to be found on the stems of the bunches, on the surface of the
grapes, on the implements of the grape gatherers! What varieties of
moulds and mildews! A vast proportion of these germs are evidently
sterilised by the wine, whose composition, being at the same time acid,
alcoholic, and devoid of air, is so little favourable to life. But is
it to be wondered at that some of these exterior germs, so numerous,
and possessing in a more or less marked degree the anaerobic character,
should find at certain moments, in the state of the wine, the right
conditions for their existence and multiplication?
* * * * *
The cause of these alterations having been found, a mode of preventing
the development of all these parasites had still to be sought.
Pasteur's first endeavour was to discover some substance which would be
antagonistic to the life of these ferments of disease, while harmless
to the wine itself, and devoid of any special smell or taste. But
in this research success was dependent on too many conditions to be
easily attainable. After some fruitless trials, the thought occurred
to Pasteur of having recourse to heat. He soon ascertained that, to
secure wine from all ulterior changes, it sufficed to raise it, for
some instants only, to a temperature of from fifty-five to sixty
degrees. His experiments were first directed upon the disease of
'bitterness.' He procured some of the best wines of Burgundy, wines
of Beaune, and of Pomard, of different years--1858, 1862, and 1863.
Twenty-five bottles were left standing forty-eight hours to allow all
the particles suspended in the wine to settle; for, however clear wine
may be, it always produces a slight deposit. Pasteur then decanted the
wine with minute care, by means of a syphon of slow delivery. This last
precaution was necessary to prevent the deposit from being stirred
up. When there remained in each bottle only one cubic centimeter of
liquid, Pasteur shook the bottle, and then examined with the microscope
the residue of each bottle. He perceived in each case distinct
filaments of ferment. The wines, however, were not in the least bitter
to the taste, but the germs of a possible evil were there--an evil
which would have been first detected by the palate when the little
fungus had fully developed.
Without uncorking it, Pasteur then heated a bottle of each of these
wines. The heating was carried to a temperature of sixty degrees (140°
Fahr.). After the cooling of the bottles he laid them by the side of
other unheated bottles of the same wines in a cellar, the temperature
of which varied in summer between thirteen and seventeen degrees. Every
fifteen days Pasteur inspected them. Without uncorking the bottles,
he held them up against the light, so that he could see the sediment
at the bottom of each bottle, and thus detect the least formation of
deposit. In less than six weeks, particularly in the wine of 1863, a
very perceptible floating deposit began to form in all the unheated
bottles. These deposits gradually augmented, and on examining them with
the microscope they were seen to be formed of organised filaments,
mixed sometimes with a little colouring matter which had become
insoluble. No deposit appeared in the heated bottles.
* * * * *