The decomposition of the sugar is therefore due to a condition of instability transferred to it from the unstable and changing ferment, and only continues so long as the decomposition of the ferment proceeds. This communication of instability from one substance undergoing chemical change to another is the basis of Liebig's conception, and is illustrated by a number of chemical analogies, one of which will suffice to explain his meaning. Platinum is itself incapable of decomposing nitric acid and dissolving in it; silver, on the other hand, possesses this power. When platinum is alloyed with silver, the whole mass dissolves in nitric acid, the power possessed by the silver being transferred to the platinum. In like manner the condition of active decomposition of the ferment is transferred to the sugar, which by itself is quite stable. The central idea is that of Stahl (p. 2) which was thus reintroduced into scientific thought. In a pure sugar solution the decomposition of the ferment soon comes to an end and fermentation then ceases. In beer wort or vegetable juices, on the other hand, more ferment is continually formed in the manner already described from the nitrogenous constituents of the juice, and hence the sugar is completely fermented away and unexhausted ferment left behind. Liebig's views were reiterated in his celebrated "Chemische Briefe," and became the generally accepted doctrine of chemists. There seems little doubt that both Berzelius and Liebig in their scornful rejection of the results of Cagniard-Latour, Schwann and Kützing, were influenced, perhaps almost unconsciously, by a desire to avoid seeing an important chemical change relegated to the domain of that vital force from beneath the sway of which a large part of organic chemistry had just been rescued by Wöhler's brilliant synthetical production of urea and by the less recognised synthesis of alcohol by Hennell (see on this point Ahrens [1902]). A strong body of evidence, however, gradually accumulated in favour of the vegetable nature of yeast, so that it may be said that by 1848 a powerful minority adhered to the views of Cagniard-Latour, Schwann, and Kützing [see Schrohe, 1904, p. 218, and compare Buchner, 1904]. Among these must be included Berzelius [1848], who had so forcibly repudiated the idea only ten years before, whereas Liebig in the 1851 edition of his letters does not mention the fact that yeast is a living organism (Letter XV). The recognition of the vegetable nature of yeast, however, by no [p010] means disproved Liebig's view of the nature of the change by which sugar was converted into carbon dioxide and alcohol, as was carefully pointed out by Schlossberger [1844] in a research on the nature of yeast, carried out in Liebig's laboratory but without decisive results.