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will lactic-acid fermentation take place. In such cases the fluid may become acid, and the acid seems to weaken and retard the lactic much more than the alcoholic fermentation. On the contrary, a neutral or alkaline state of the fluid greatly promotes the lactic.

To make this clear, add magnesia to the said sugar mixture, and the two kinds of fermentation will commence together, whilst lactate of magnesia will be precipitated in crystals, and the microscope will detect globules of beerbarm and milk-barm mixed. The latter arises in the albuminous fluid where the alkalinity restrains the power of the alcoholic fermentation. A slightly alkaline medium is very suitable to the formation of the new barm, but also favours the growth of Infusoria, which consume the young globules, or at least hinder their further development by laying an embargo on all the nutriment.

In an alkaline fluid, the beer-barm works feebly, often not at all. Acids, even in very minute quantity (contrary to the received opinion), hinder its action. It requires a neutral medium, which should be secured in experiments on a small scale; in a commercial view, this rule does not hold, for neutrality also promotes lactic fermentation.

We are at least, then, sure that fermentation in general, and the lactic, with which we are concerned, in particular, is subject to manifold alterations, some as yet unknown, some known, but inevitable upon various influences. To obviate these last, a medium is wanted, which, on the one hand, favours the growth of the milk-barm mycoderms; and on the other hand is apt to hinder other mycoderms and infusoria.

Such a medium is onion-juice. The volatile oil of raw onions has the property of repressing the development of the beer-barm mycoderm, which usually associates itself with that of the milk-barm.

If globules of the beer-barm be sown in raw onion juice, alcoholic fermentation never commences, and the mycoderm is not developed. But if the juice be boiled to drive off the oil, and when cold, beer-barm be mixed with it, the myco

derm is developed with incredible rapidity, and separates the sugar of the juice into alcohol and carbonic acid.

We now turn to the vinous or tartaric alcoholic (?) fermentation. (Weinsauren).

Tartrate of lime mixed with any organic substance and left to itself under water, very soon ferments. N llner, a manufacturing chemist, thought he discovered in this process a new acid, which proved, in the hands of Nikles, Dumas, and others, to be identical with the metaceton-acid discovered by Gottlieb from the action of potash on sugar.

Pasteur chose for his experiments, not tartrate of lime but of ammonia. This change of the basis brought out various and wonderful changes; but our business being to investigate the cause of this fermentation, we leave these last untouched and proceed.

Dissolve pure tartrate of ammonia in distilled water; add any nitrogenous albuminous substance soluble in water a fresh vegetable extract, any animal fluid, or dissolved beer-barm, in the proportion of 0 or 30' part of the whole by weight. Heat the mixture, fill a bottle to the neck, and when the temperature is reduced to 30 centigrade, add to it a cubic centimètre of ordinary turbid fermenting must. The quantity of solid matter which is sown in this manner is almost imponderable, yet causes immense effects. Under favorable conditions of warmth, neutrality, &c., the fluid grows turbid in a few hours, and the fermentation makes itself known next day by giving out gas; the disturbance goes on increasing, and a sediment gradually forms at the bottom of the bottle, but continues very small in proportion to the tartrate. By an optical test it is easy to ascertain that the tartaric acid has been altered into products which no longer exercise any influence on polarized light. That is, whilst dissolved ordinary tartaric acid turns the plane of polarization to the right (hence called "dextro-tartaric ") and dissolved lævo-tartaric acid to the left, the product of the above experiment does not turn it either way; and this is the paratartaric, or ordinary racemic acid. If this wine-barm sediment (which is granular and like strings of pearls) is well rinsed in water, and put

into a fresh solution of tartrate of ammonia, a fresh fermentation commences in a few hours.

The acids above mentioned, as dextro-tartaric and lævotartaric (also called dextro-racemic and lævo-racemic) afford a curious instance of specific difference, depending on the above optical contrariety, besides the fact that their respective crystals are not identical, but the very reverse of each other; like an engraving compared with the copper-plate, or a face with the image in a mirror, no chemical difference exists.

It was extremely interesting to ascertain whether the lavotartaric suffers the same change by fermentation as the ordinary or dextro-tartaric; which, in the above experiment, lost the power of rotating the plane of polarization.

[N.B.-As far as Roth can be understood, this altered and optically inert acid consists of an atom of each of the two tartaric acids.]

By an exactly similar experiment, it was found, by using lævo-tartrate of ammonia, instead of ordinary tartrate, the difference here again was merely optical. The latter experiment gave a sediment, which at first was optically inert, but after some days resumed the left-hand power; whereas the product of the ordinary tartrate lost its right-handed power for ever!

Nothing is easier than in this marvellous way, where an organised being acts the part of the most refined chemical reagent, to produce lævo-tartaric acid, by the pound, to any amount. But it is a far more important fact that we see a molecular dissymmetry related to organic bodies stepping in, during a physiological phenomenon, and altering a chemical affinity. For hitherto, the above effect on polarized light has only been seen in such organic combinations as are either generated by a vital process, or else, at least, proceed from combinations that have thus originated.

Clearly, the atomic arrangement is the only means of diagnosis in the two tartaric acids, and nevertheless we see that the dextro alone is fermentible, whilst the lævo undergoes no change.

"Amassons les faits," says Buffon, "pour avoir des idées ;" so let us follow Pasteur on his voyages of discovery.

Thus he discovered that succinic acid is a normal product of alcoholic fermentation, formed at the expense of the sugar to the amount of at least per cent. Two processes are given for procuring the product which has for so many centuries escaped notice; and a third for obtaining it from wine itself.

Another discovery of Pasteur's in this process is glycerine, found in proportion of 3 per cent. to the sugar.

He also found (contrary to the prevalent opinions) that an appreciable quantity of lactic acid is also found during alcoholic fermentation, though it is the product of a totally different fermentation synchronously carried on. But this is only under very peculiar circumstances.

Since Lavoisier, we have known that, in alcoholic fermentation the fluid always reacts as an acid. But, if lactic acid be only exceptional, whence comes the invariable acidity attending alcoholic fermentation? This and the succinic acid, invariably present, gives the answer-as invariably, with glycerine, as the very alcohol and carbonic acid.

The universal chemical doctrine of the formation of ammonia at the expense of the beer-barm, upon which also rests Liebig's explanation of fermentation is set aside by Pasteur, who, adopting Boussingault's method, with minute doses of ammonia, decided positively that even that small quantity entirely disappears during fermentation.

Proof of the organic, vital, living, power of the barm.

To a solution of raw sugar was added, on the one hand, tartrate of ammonia, on the other hand, some mineral substances (phosphates) which are constituents of the beerbarm, with an imponderable quantity of barm-globules. The globules sown under these circumstances developed and multiplied as the sugar fermented, whilst the minerals gradually dissolve, and the ammonia disappears. In other words, the ammonia changes into that albuminous substance which is a constituent of the barm, whilst the phosphates give their mineral principles as food for the new globules.

As for the carbon, that is undeniably supplied by the

sugar.

If from the constituents of the medium in which the living seeds of the beer-barm are to develop, you take away either the phosphates, or the ammoniacal salt, or both at once, then the globules do not multiply, as no fermentation takes place. It is immaterial whether the salts of ammonia be from the mineral or organic kingdom; so also the phosphates may be derived from the burnt ash of the ordinary beer-barm, or an originally pure chemical precipitate. Nothing affects the efficiency of the barm but the supply of suitable nutriment.

In another ease, crystallized sugar was used instead of raw, and dissolved in distilled water; the nitrogenous matters, usually employed in fermentation, were omitted; mere phosphates and ammoniacal salts, i. e. nothing but mineral substances. Whether carbonate of lime (chalk) was added or withheld, made no difference; when the smallest quantity of barm was sown in this medium, the fermentation appeared just as soon as if gluten, caseine, animal membrane, &c., had been employed to aid it.

Thus it is incontrovertibly proved that the cause of fermentation must not be sought in the ammonia, nor in the nitrogenous matters, which are mere nutrients of the barm, and that this last is no chemical precipitate, but an organised living being, whilst fermentation is a physiological action, and not a chemical inert process.

1859. The invariable presence of a barm (milk-barm) when sugar is converted into lactic acid, having been established by Pasteur in 1858, with the fact that nitrogenous matter promotes the change simply by feeding the barm mycoderm; this last has to be examined strictly. The globules are smaller than the others, viz. millimètre in diameter, and swollen at each end, and are incapable of producing any fermentation but its own (the lactic acid). Their organic nature was proved as follows:-A small quantity of ammoniacal salt, phosphate and precipitated carbonate of lime, were mixed with pure eau sucrée. In twenty-four hours the

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