Part 10

'I would undertake in the space of twenty-four hours to cover with mycoderma aceti a surface of vinous liquid as large as the hall in which we are here assembled. I should only have to sow in it the day before almost invisible particles of newly-formed mycoderma aceti.'

Let the reader try to imagine the millions upon millions of little mycoderma particles which would come to life in that one day.

But how is the mycoderm seed to be obtained in the first instance? Nothing more simple. The mycoderma aceti is one of those little so-called 'spontaneous' productions which are sure to appear of themselves on the surface of liquids or infusions suitable to their development. In wine, in vinegar, or suspended in air, everywhere around us, in our towns, in our houses, there exist germs of this little plant. If we wish to procure some fresh mycoderm it is only necessary to put a mixture of wine and vinegar into a warm place. In a few days, generally, if not always, there appear here and there little greyish patches scattering the light instead of regularly reflecting it, as does the surrounding liquid. These specks go on increasing progressively and rapidly. This is the mycoderma aceti raised from the seeds which the wine or the added vinegar contained, or which the air deposited; just as we see a field covered with divers weeds by seeds naturally distributed in the earth, or which have been brought to it by the wind or by animals. Even in this last circumstance the comparison holds good, for after you have put wine or vinegar in a warm place there soon appear, whence we know not, little reddish flies, so commonly seen in vinegar manufactories, and in all places where vegetable matter is turning sour. With their feet, or with their probosces, these flies transport the seed.

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At Orleans the process for the manufacture of vinegar is very simple. Barrels ranged over each other have on each of their vertically-placed bottoms a circular opening some centimeters in diameter, and a smaller hole adjacent, called fausset, for the air to pass in and out when the large opening is closed, either by the funnel, through which the wine is introduced, or by the syphon, which is used for drawing off the vinegar. These barrels, of which the capacity is 230 litres, are half filled. The manual labour consists in keeping up a suitable temperature in the vessel, and in drawing from it every eight days about eight or ten litres of vinegar, which are replaced by eight or ten litres of wine.

A barrel in which this give-and-take of wine and vinegar goes on is technically called a 'mother.' The starting of a 'mother' is not a rapid process. We begin by introducing into the barrel 100 litres of very good and very limpid vinegar; then two litres only of wine are added. Eight days after, three litres of wine are added, a week later four or five, until the barrel contains about 180 to 200 litres. Then for the first time vinegar is drawn off in sufficient quantity to bring back the volume of the liquid to about 100 litres. At this moment the labours of the 'mother' begin. Henceforward ten litres of vinegar may be drawn off every eight days, to be replaced by ten litres of wine. This is the maximum that a cask can yield in a week. When the casks work badly, as is often the case, it is necessary to diminish their production.

This Orleans system has many drawbacks. It requires three or four months to prepare what is called a 'mother,' which must be nourished with wine very regularly once a week under penalty of seeing it lose all its power. Then it is necessary to continue the manufacture at all times, whether the vinegar be required or not. To reconstitute a 'mother,' one must begin from the very beginning, a process which involves a loss of three or four months' time. Lastly--a condition which is at times very inconvenient--a 'mother' cannot be transported from one place to another, or even from one part of the same locality to another. The 'mother,' in fact, must rest immovable.

Pasteur advised the suppression of the 'mothers.' He recommended an apparatus, which is simply a vat, placed in a chamber the temperature of which can be raised to 20° or 25° Centigrade. In these vats vinegar already formed is mixed with wine. On the surface is sown the little plant which converts the wine into vinegar. The mode of sowing it has been already explained. The acetification begins with the development of the plant.

A great merchant of Orleans, who had from the first adopted Pasteur's process, and who had won the prize offered by the 'Society for the Encouragement of National Industry' for a manufactory perfected after these principles, has stated that at the end of nine or ten days, sometimes even in eight, all the acetified wine is converted into vinegar. From a hundred litres of wine he drew off ninety-five litres of vinegar. After the great rise of temperature observed at the moment of the formation of the vinegar, and which is caused by the chemical union of the alcohol and the oxygen of the air, the vinegar is allowed to cool. It may then be drawn from the vat, introduced into barrels, refined, and straightway delivered, fit for consumption. When the vat is quite emptied, and well cleaned, a new mixture is made of vinegar and wine, the little plant is sown as before, and the same facts are reproduced in the second as in the first operation.

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In the vessels where vinegar is preserved, whether in the manufactories, in private houses, or in grocers' shops, it often happens that the liquid becomes turbid, and impoverished in an extraordinary manner; it even ends in putrefaction, if a remedy be not promptly applied. Pasteur has pointed out the cause of these phenomena. After the alcohol has become acetic acid by the combustive action of the mycoderm, the question remains, what becomes of the mycoderm? Most frequently it falls to the bottom of the vessel, having no more work to accomplish. This is a phase of the manufacture which must be watched with care. It is shown by the experiments of Pasteur that the mycoderma aceti can live on vinegar already formed, maintaining its power of fixing the oxygen on certain constituents of the liquid. In this case the acetic acid itself is the seat of the chemical action--in other words, the oxygen unites with the carbon of the acetic acid, and transforms it into carbonic acid, and as the acetic acid has a composition which can be represented by carbon and water, it follows that if the combustion is allowed to take its course, instead of vinegar we have eventually nothing but water mixed with a small proportion of nitrogenous and mineral matters, and the remains of the mycoderm. We have thus an ordinary organic infusion exempt from all acidity, and one which could not be better fitted to become the prey of the vibrios of putrefaction or of the aérobic mucors. By these mucors, moreover, which form a film on the surface of the liquid after the mycoderm has fallen, the anaérobic vibrios, protected from the action of the air, can come into active existence. Here we find ourselves in presence of one of those double phenomena, of putrefaction in the deeper parts of the liquid, and of combustion at the surface which is in contact with the air. Nothing is more prejudicial to the quality of the vinegar than the setting in of this combustion after the vinegar has been formed, and when it contains no more alcohol. The first materials of the vinegar upon which the oxygen transmitted by the mycoderm fixes are, in fact, the ethereal and aromatic constituents which give to vinegar its chief value.

Another cause of the deterioration of the quality of vinegar, which is sometimes very annoying to the manufacturer, consists in the frequent presence of little eel-like organisms, very curious when viewed with a strong magnifier. Their bodies are so transparent that their internal organs can be easily distinguished. These eel-like creatures multiply with extraordinary rapidity. Certainly there is not a single barrel of vinegar manufactured by the Orleans system which does not contain them in alarming numbers. Prior to Pasteur's investigations, the ignorance regarding these organisms was such that they were actually considered necessary to the production of the vinegar; whereas they are, on the contrary, most inimical to it, and must, if possible, be got rid of. This is, moreover, rendered desirable by the repugnance which is naturally felt to using a liquid defiled by the presence of such animalcules--a repugnance which becomes almost insurmountable to anyone who has once seen through a microscope the swarms contained in a drop of vinegar. The mischief wrought by these little beings in the manufacture of vinegar results from the fact that they require air to live. The effect can easily be perceived by filling to the brim a bottle of vinegar, corking it, and then comparing it with a similar bottle half filled with the same vinegar, and left uncorked in contact with the air. In the first bottle, the motions of the eel-like creatures become gradually slower, until after a few days they cease to multiply and fall lifeless to the bottom of the vessel. In the second bottle, on the contrary, they continue to swarm and move about. This need of oxygen is further demonstrated by the fact that, if the vinegar reaches a certain depth in the bottle, life is suspended in the lower parts, and the little eel-like organisms, in order to breathe more freely, form a crawling zone in the upper layers of the liquid.

Connecting these observations with the other fact that the vinegar is formed by the action of the mycodermic film on its surface, we can understand at once that the mycoderm and the little eels continually carry on a struggle for existence, since both of these living things--the one animal the other vegetable--imperiously demand the same aliment, oxygen. They live, moreover, in the same superficial layers, a circumstance which gives rise to very curious phenomena. When, for one reason or another, the film of mycoderm is not formed, or when there is any delay in its production, the little eels invade in such great numbers the upper layers of the liquid that they absorb all the oxygen. The little plant has in consequence great difficulty in developing itself or even in beginning its life. Reciprocally, when the work of acetification is active, and when the mycoderm has occupied the upper layers, it gradually drives away the eels, which take refuge, not deep down, where they would perish, but against the moist sides of the barrel or the vat. There they form a thick whitish scum all in motion. It is a very curious spectacle. Here their enemy, the mycoderm, can no longer injure them to the same extent, since they are surrounded with air; and here they wait with impatience for the moment when they can again take their place in the liquid, and, in their turn, fight against the mycoderm. In Pasteur's process, where the vats are very often cleansed, it is easy to keep them free from these little animalcules; they have not time to multiply to a hurtful extent. Indeed, if the operation be well conducted, they do not make their appearance at all.

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Nearly all Pasteur's publications have had from the moment of their appearance to undergo the severest criticism. Their novelty caused them to clash with the prejudices and errors current in science. His researches on fermentation provoked lively opposition. Liebig did not accept without recrimination a series of researches which concurred in upsetting the theory he had enunciated and defended in all his works. After having kept silence for ten years, he published, at Munich, where he was professor, a long memoir entirely directed against Pasteur's results. In 1870, on the eve of the war, Pasteur, who was at that time returning from a scientific journey into Austria, determined to pass by Munich, with the view of attempting to convince his distinguished adversary. Liebig received him with great courtesy, but, hardly recovered from an illness, he alleged his convalescence as a reason for declining all discussion.

Then followed the Franco-German war. Hardly was it terminated when Pasteur brought before the Academy of Sciences at Paris a defence of what he had published, as a sort of challenge to his illustrious opponent. The memoir of Liebig was filled with the most skilful arguments.

'I pondered it for nearly ten years before producing it,' he wrote. Pasteur, putting aside all subtleties of argument, went straight to the two objections of the German chemist which lay at the root of the discussion.

It may be remembered that one of the most decisive proofs by which Pasteur overthrew Liebig's theory resulted from the experiments in which by the aid of mineral bodies and fermentable matter he produced a special living ferment for each definite fermentation. By removing all nitrogenous organic matter, which in Liebig's theory constitutes the ferment, Pasteur established, at one and the same time, the life of the ferment and the absence of all action of albuminoid matter in process of alteration. Liebig here formally contested the fact that Pasteur had been able to produce yeast and alcoholic fermentation in a sweetened mineral medium by sowing therein an infinitesimal quantity of yeast. It is certain that, ten years previously, when Pasteur announced the production of yeast life and alcoholic fermentation under such conditions, his experiment was one so difficult to perform that it sometimes happened to Pasteur himself to be unable to reproduce it. The cells of yeast sown in the sweetened mineral medium found themselves often associated with other microscopic organisms, which were singularly hurtful to the life of the yeast. Pasteur was at this period far from being familiarised with the delicacy which such experiments require, and he did not yet know all the precautions indicated later on, which were indispensable to success. Though in his original memoir of 1860 Pasteur had pointed out the difficulties of his experiment, these difficulties existed nevertheless. Liebig took hold of them with skill, exaggerated them; saw, so to speak, nothing but them; and declared that the results announced never could have been obtained. But in 1871 the fundamental experiment of Pasteur, on the life of yeast in a sweetened mineral medium, had become a trifle for him. He knew exactly how to form media deprived of all foreign germs, how to prepare pure yeast, and how to prevent the introduction of new germs, which could develop in the liquids and hinder the life of the yeast.

'Choose,' said he to Liebig, 'from the members of the Academy one or several, and ask them to decide between you and me. I am ready to prepare before you and before them, in a sweetened mineral medium, as much yeast as you can reasonably ask for, and with substances provided by yourself.'

Liebig's second objection had reference to acetic fermentation. The process of acetification known as that of 'beech shavings' is widely practised in Germany and even in France. It consists in causing alcohol diluted with water and with the addition of some millièmes of acetic acid to trickle slowly into barrels or vats filled with shavings of beech, either massed together without order or disposed in layers after having been rolled up like the spring of a watch. Openings formed in the sides of the barrel, and in a double bottom upon which the shavings rest, permit the access of the air, which rises into the barrel as it would in a chimney, and yields all or part of its oxygen to the alcohol to convert it into acetic acid. All writers prior to Pasteur, and Liebig in particular, maintained that the shavings acted like porous bodies in the same manner as finely divided platinum. The acetic acid, they said, was formed by a direct oxidation, without any other influence than the porosity of the wood. This view of the subject was rendered plausible by the fact that in many manufactories the alcohol employed is that of distillation, which contains no albuminoid substances. Moreover, the duration of the shavings is in a sense indefinite.

According to Pasteur, the shavings perform only a passive part in the manufacture. They promote the division of the liquid and cause a considerable augmentation of the surface exposed to the air. They moreover serve as a support for the ferment, which is still, according to him, the mycoderma aceti, under the mucous form proper to it when submerged.

Certainly appearances were far from being favourable to this view. When the shavings of a barrel which has been in work for several months or even for several years are examined, they are found to be extraordinarily clean. It might be said that they had just been carefully washed. Pasteur has shown that this is but a deceptive appearance, and that in reality these shavings are partly or wholly covered with a mucous film of mycoderma aceti of excessive tenuity. It is necessary to scrape the surface of the wood with a scalpel and examine the scrapings with the microscope to be assured of the presence of this pellicle.

Liebig, who somewhere speaks, not without a certain contempt, of the microscope, denied formally the exactitude of these assertions.

'With diluted alcohol, which is used for the rapid manufacture of vinegar,' he wrote, 'the elements of nutrition of the mycoderm are excluded, and the vinegar is made without its intervention.' He asserted also in his memoir of 1869 that he had consulted the head of one of the principal manufactories of vinegar in Germany, that in this manufactory the diluted alcohol did not receive during the whole course of its transformation any foreign addition, and that beyond the air and the surfaces of wood and charcoal--for charcoal is sometimes associated with the beech shavings--nothing can act upon the alcohol. Liebig added that the director of the manufactory did not believe at all in the presence of the mycoderm, and that finally he, Liebig, in examining the shavings which had been used for twenty-five years in the manufactory, saw no trace of mycoderm on their surface.

The argument appeared conclusive. How, in fact, could we understand the production of a plant containing within itself nitrogen and mineral elements which was nevertheless to be nourished by water and alcohol.

'You do not take into account,' replied Pasteur, 'the nature of the water which serves to dilute your alcohol. This water, like all ordinary waters, even the purest, contains salts of ammonia and mineral matters which are capable of nourishing the plant. Finally, you have not rightly examined with the microscope the surface of the shavings, otherwise you would have seen the little particles of the mycoderma aceti united, in some cases, to a thin film which can even be lifted up. I propose to you, moreover, to send to the Academic Commission charged with the decision of the debate, some shavings that you have obtained yourself in the manufactory at Munich, and in the presence of its director. I will undertake to prove before the members of the commission the presence of the mycoderm on the surface of these shavings.'

Liebig did not accept this challenge. To-day the question is decided.

THE QUESTION OF SPONTANEOUS GENERATION.