Pasteur and his work : from an agricultural and veterinary point of view / by George Fleming.

  • Fleming, George, 1833-1901.
Date:
1886
Catalogue details

Licence: Public Domain Mark

Credit: Pasteur and his work : from an agricultural and veterinary point of view / by George Fleming. Source: Wellcome Collection.

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    ing a little yeast in some water, filtering the liquid, dissolving in this some sugar, and then dropping carefully into it a minute quantity of fermenting milk, to act as the seed of the ferment in the limpid saccharine solution. Next day the pellucid fluid had become turbid, because of the active fermentation which had been commenced, and as the chalk dissolved, a deposit took place which the microscope showed was composed of germinating rods of the organism jnst alluded to—the lactic ierment. In another experiment, he substituted for the yeast- water a clear decoction of nitrogenous matter, but the ferment invariably appeared in the same manner. In order to effectually silence the partisans of Liebig’s theory, and indeed of all chemists, as to the accidental presence of the organised ferment, the cells of which, they asserted, perished during fermentation and formed lactate of ammonia, Pasteur unremittingly laboured to demonstrate the falsity of the theory, and to prove that not only was there no ammonia formed during alcoholic fermentation, but if it were added it disappeared, entering into the formation of the new cells. Two notable characteristic and crucial experiments he made, which finally settled the dispute. One was with regard to the yeast of beer or alcohol, and the other to the lactic ferment. He introduced into a pure solution of sugar a small quantity of a crystalline salt of ammonia, and some phosphates of potash and magnesia ; into this mixture, which, it will be observed, was destitute of albuminoid matter, he sowed an imponderable quantity of yeast—the living cells of the lactic fermentation. The cells thus sown germinated and multiplied, the sugar fermented, and the phosphorus, magnesium, and potassium of the salts united with elements of the sugar of milk, and were in the end con¬ verted into lactic acid. A second experiment made with the same skill and care yielded the same results, and demolished the theory of Berzelius and Liebig, which had no longer any foundation. The whole process took place between the sugar aud the ferment germ—a living organism—which owed its growth and multiplication to the nutriment it found in the sugar: fermentation, in short, was simply a phenomenon ol nutrition, the ferment contriving to grow upon the sugar and the mineral salts, the remaining portions of these combining to form, in fermenting milk, alcohol and lactic acid, and in the saccharine fermentation alcohol and acetic acid. The results of his experiments, and the conclusions he arrived at from a consideration of them, Pasteur laid before the Academy of Sciences in 1857. By the light of his discovery of the lactic ferment, Pasteur soon found a new ferment—the butyric, which has its own special fermentation, resulting in the production of butyric acid. This