Codex @codex  0

Original memoir by Louis Pasteur, Annales scientifiques de l’École Normale Supérieure, first series, volume 1, pages 113–158. DOI: doi.org/10.24033/asens.4. The numbered sections discuss acetification, the surface growth and experimental conditions.

Original article: www.numdam.org/article/ASENS_1864_1_1__113_0.pdf

Original memoir by Louis Pasteur, communicated in 1857 and printed in 1858; available here in the collected works, volume II, pp. 3–13. §II gives inoculation and growth experiments and contrasts the rival chemical theory.

The yeast plant is a fungus, whereas the characteristic vinegar-forming organisms are acetic acid bacteria. Calling both vegetable growths reflects an older classification of microscopic organisms; it does not make them green plants or two stages of one species.

The familiar brewing and baking yeast is Saccharomyces cerevisiae. Its oval or rounded cells possess a cell wall, cell membrane, cytoplasm, cell nucleus and other eukaryotic structures. Ordinary multiplication is by budding: a small outgrowth enlarges, nuclear division supplies it, and separation leaves a scar or a temporary attached cluster. Under suitable conditions, the life cycle also includes mating between compatible haploid cells and formation of spores by diploid cells. Those processes are distinct from simply breaking a chain of accidentally adherent cells. Neither roots nor a leaf-like apparatus is required for its growth.^[ref]

Yeast obtains organic nutrients from its surroundings. In alcoholic fermentation it converts fermentable sugar into ethanol and carbon dioxide; the idealized glucose balance isA real culture also uses material to build cells and produces additional compounds. The process does not require oxygen as a reactant in that net balance, although yeast can respire and its growth and product yields depend on conditions. In bread the gas expands the dough; in a fermenting liquid both gas evolution and chemical change can be followed. Gas bubbles alone do not identify the organism responsible.

The historical vinegar plant or mother of vinegar appears as a surface film or gelatinous mass in a suitable alcoholic liquid. Louis Pasteur used the name Mycoderma aceti for the film-forming agent in his investigations of acetification. In modern terms, members of several acetic-acid-bacterial groups can occur in vinegar cultures. Rod-shaped bacterial cells reproduce by binary fission; some form an extracellular, often cellulose-rich, matrix that helps produce a visible pellicle. The gross mother is therefore a growth structure or microbial community, not a single large cell and not necessarily a pure culture of one modern species.^[ref]

Its essential chemical role is oxidation of ethanol to acetic acid using atmospheric oxygen:Thus the historical term acetic fermentation denotes an oxidative microbial process, unlike the oxygen-independent net alcoholic-fermentation reaction above. Surface access to air favours the process. With suitable organisms and conditions, further oxidation of the acid can occur, so indefinitely leaving an exhausted culture exposed to air does not guarantee indefinite accumulation of vinegar.

Louis Pasteur's Mémoire sur la fermentation acétique by Louis Pasteur, published in 1864, supplies contemporary experimental evidence appropriate to this paper. Inoculating an appropriate alcoholic medium with material from an active film, observing film development and measuring the rise of acidity connects the growth with the chemical process. Comparisons with uninoculated or differently aerated preparations distinguish mere atmospheric exposure from the action of the growth. His experiments also examined the effects of submergence and the conditions under which the film performed acetification.^[ref]

Wine turning to vinegar therefore illustrates succession: yeast can first supply an alcoholic substrate from sugar, and acetic acid bacteria can then oxidize that substrate when oxygen is available. A white surface growth is not automatically the active vinegar agent; other yeasts and moulds can form films or spoil the liquid. Microscopy, controlled transfer and chemical measurement together provide a natural-history account stronger than identifying every surface skin by its household name.

The names are historical microscopic groupings, and the central dispute is whether the organisms cause the chemical changes, arise as their products, or merely grow in the altered liquid. Those are different causal propositions. Seeing small moving bodies in a fermenting infusion does not by itself choose among them.

Infusoria were organisms encountered in infusions of organic material. Many recognizable examples are now classified as ciliates or other unicellular eukaryotes, with a cell nucleus, organized feeding structures and locomotory cilia or flagella. Historical usage could extend much more widely than a modern taxonomic group. Some organisms found in an infusion feed on the bacteria already growing there; their later appearance can thus reflect ecological succession rather than production of the first chemical change.

Vibriones commonly denoted minute actively moving, often elongated, curved or sinuous forms. It does not follow that every historical vibrion belongs to the modern genus Vibrio. Bacteria, in some nineteenth-century classifications, meant a narrower set of minute rod-like bodies than the present bacterial domain. In modern terms bacteria are prokaryotes, lacking a membrane-bound cell nucleus; they generally multiply by binary fission. Shape and apparent movement alone do not establish their species. Brownian motion of nonliving particles also must not be mistaken for independent locomotion.

Three positions illustrate the debate available in 1866:

The decisive experimental question is not whether fresh air is present, but what accompanies it. In a curved-neck flask, a boiled nutrient liquid remains in communication with air while much airborne dust settles in the neck. An otherwise comparable preparation can be exposed by breaking the neck or bringing trapped material into contact with the liquid. The comparison tests whether access of contaminating material, rather than air as such, permits growth and putrefaction. Heat treatment, the preparation's composition, possible surviving resistant forms and accidental contamination all affect interpretation. A negative culture under one condition is not a universal proof about the origin of life.^[ref]

Modern fermentation is an enzyme-mediated metabolic process; putrefaction commonly involves microbial degradation of nitrogenous organic matter, with mixed and sometimes foul-smelling products. Organisms can be causal agents, and their products can subsequently feed other organisms. Thus the two directions of influence need not be mutually exclusive in a mixed infusion. The mere coexistence of bacteria, ciliates, gas and odour supplies much weaker evidence than controlled inoculation, time-resolved microscopy and chemical measurement.

A later qualification is essential. Eduard Buchner's cell-free fermentation experiments, first reported in 1897 and described in his 1907 lecture, showed that an extract of yeast could carry out alcoholic fermentation without intact living yeast cells. This supports chemical machinery made by organisms; it does not restore the earlier indiscriminate decomposition-by-contact hypothesis. These later findings must not be put into an 1866 candidate's mouth.^[ref]

Original memoir by Louis Pasteur; atmospheric particles, boiled liquids, curved-neck flasks and the spontaneous-generation controversy.