Buchner's discovery was not received without some hesitation. A number of investigators prepared yeast-juice, but failed to obtain an active product [Will, 1897; Delbrück, 1897; Martin and Chapman, 1898; Reynolds Green, 1897; Lintner, 1899]. A more accurate knowledge of the necessary conditions and of the properties of yeast-juice, however, led to more successful results [Will, 1898; Reynolds Green, 1898; Lange, 1898], and it was soon established that, given suitable yeast, an active preparation could be readily procured by Buchner's method. Criticism was then directed to the effect of the admitted presence of a certain number of micro-organisms in yeast-juice [Stavenhagen, 1897], but Buchner [Buchner and Rapp, 1897] was able to show by experiments in the presence of antiseptics and with juice filtered through a Chamberland candle that the fermentation was not due to living organisms of any kind. The most weighty criticism of Buchner's conclusion consisted in an attempt to show that the properties of yeast-juice might be due to the presence, suspended in it, of fragments of living protoplasm, which, although severed from their original surroundings in the cell, might retain for some time the power of producing alcoholic fermentation. This, it will be seen, was an endeavour to extend Nägeli's theory to include in it the newly discovered fact. In favour of this view were adduced the similarity between the effects of many antiseptics on living yeast and on the juice, the ephemeral nature of the fermenting agent present in the juice, the effect of dilution with water, and the phenomenon of autofermentation which is exhibited by the juice in the absence of added sugar [Abeles, 1898; v. Kupffer, 1897; v. Voit, 1897; Wehmer, 1898; Neumeister, 1897; Macfadyen, Morris, and Rowland, 1900; Bokorny, 1906; Fischer, 1903; Beijerinck, 1897, 1900; Wroblewski, 1899, 1901]. A brief general description of the actual properties of yeast-juice and of the phenomena of fermentation by its means is sufficient to show the great improbability of this view. The juice prepared by Buchner's method forms a somewhat viscous opalescent brownish-yellow liquid, which is usually faintly acid in reaction [compare Ahrens, 1900] and almost optically inactive. It has a specific gravity of 1·03 to 1·06, contains 8·5 to 14 per cent. [p020] of dissolved solids, and leaves an ash amounting to 1·4 to 2 per cent. About 0·7 to 1·7 per cent. of nitrogen is present, nearly all in the form of protein, which coagulates to a thick white mass when the juice is heated.