Page:Popular Science Monthly Volume 25.djvu/233

Rh The weights as applied gave a uniform pressure; but the cover, as will be seen from the table, did not settle at a uniform rate. There was a fall of 5° in temperature during the first three days, then followed a gradual but not uniform rise, until the maximum of 87° was reached at the end of the first week. It will likewise be noticed that a variation of but 5° from the initial temperature occurred during the first three weeks after the cover was put on and weighted, and that the fall in the temperature was not uniform.

Experiments were repeatedly made with samples of ensilage, taken through the tube, from the interior of the silo. The samples obtained on the 9th of September swarmed with bacteria, which were remarkably active and rapidly increasing by self-division. After the first few days the indications of rapid reproduction were not so marked, but the activity of the bacteria was not sensibly diminished until the temperature had fallen below 60°, more than two months after the silo was filled. The variations in temperature and in the rate of settling were undoubtedly connected with the vital activity of the bacteria, but the precise relation of these variations could not be traced.

The real significance of these minute organisms can not be fully appreciated without a review, including a brief history, of the known facts of the process of

—The alchemists were acquainted with ferments and fermentation as early as the thirteenth century, but we need not stop to notice their crude theories in regard to the process. In 1659, Willis, an English physician, presented a theory of fermentation, which was revived by Stahl, the originator of the phlogiston theory, in 1697. According to the theory of these philosophers, ferments had a peculiar motion of their particles which they communicated to the particles of fermentable substances and thus produced fermentation. The discovery of carbonic acid by Black (1752), of oxygen by Priestley (1774), and of the composition of the atmosphere and water by Cavendish (1781), laid the foundation for the experiments of Lavoisier, who attempted a quantitative determination of the changes taking place in the transformation of sugar into alcohol. Gay-Lussac (1815) revised the figures obtained by Lavoisier, by less perfect methods, and made a close approximation to a correct formula. In 1828 Dumas and Boullay pointed out and corrected errors in the formulæ of Gay-Lussac, and in this amended form they were, for many years, accepted as an accurate statement of the phenomena of alcoholic fermentation. Afterward, however, the discovery was made that glycerine and succinic acid are constant products of the process, and the formulæ had to be again corrected. These formulæ, even in their amended form, did not take into the account the yeast which had been recognized as an essential element in the process, and theories were formed to account for its action. Berzelius attributed the influence of yeast to a "catalytic" action—mere contact with the ferment being sufficient to excite