HISTORICAL INTRODUCTION. 459 



either alone or associated with carbon dioxide, could be demon- 

 strated in the case of higher plants and in fruits in the absence of 

 yeast cells. Under this category may be ranked the publications 

 of SCHUNCK (I.) and Duclaux. the former of whom found that 

 alcohol, succinic acid and carbon dioxide occur during the so-cnlled 

 fermentation of madder though, as the author himself admitted, 

 the collaboration of living micro-organisms was not precluded. 

 The observation of DUCLAUX (XVIII.) respecting the production 

 of alcohol in an alkaline sugar solution has been mentioned in 

 vol. i, p. 25. We may also refer here to the observations of 

 WILL (XXXV.), who desiccated yeast at a low temperature and 

 detected fermentation phenomena, but not growth, on examining 

 the samples after nine years' storage. 



Thus, during the prolonged discussion on the nature of 

 fermentation previous to the year 1896, opinion had gradually 

 veered round again in favour of the enzyme theory. The 

 experimental proof, however, that the fermentative agent is 

 separable from the living cell, and that consequently the decom- 

 position of sugar into alcohol and carbon dioxide should be 

 regarded as a purely chemical reaction, must nevertheless rank as 

 a new and important fact. This proof was afforded in a simple 

 and precise manner by E. BUCHNER (II.) towards the close of 

 1896, in that, by purely mechanical means, after breaking down 

 and removing the cell membranes and the protoplasmal envelope, 

 he obtained the cell contents by themselves, in the form of juice 

 capable of decomposing sugar, and in a practically cell-free 

 condition. Although this discovery has become of the greatest 

 theoretical importance and roused considerable attention in the 

 fermentation industry, it does not seem adapted for direct 

 technical application, so long as the yeast cell has to be drawn 

 upon as the source of the enzyme, owing to the roundabout 

 character of the method. This view was also adopted by 

 WORTMANN (XVIII.) in connection with the fermentation of 

 wine, in which the entire metabolism of the living yeast comes 

 into play. E. FISCHER (VI.) expressed great approbation of the 

 discovery. The practical application of the method and the 

 preparation of permanent yeast are described in 320; and the 

 method of preparing the yeast juice by crushing and pressing the 

 cells has found suitable application through the labours of 

 H. HAHN (II.), MAZE (II.), TAKAHASHI (I.), WEINLAND (I.), 

 KOHNSTAMM (I.), CZAPEK (V.), SxoKLASA (HI.) and his colleagues 

 COHNHEIM (I.), KRASNOSSELSKY (II.) and MAXIMOW (I.). 



317. Preparation of Expressed Yeast Juice. 



The method of preparing expressed yeast juice was originally 

 elaborated at the Munich Hygienic Institute, valuable assistance 

 being afforded by M. Hahn, who recommended the use of kie- 

 selguhr and the hydraulic press. The operation is divided into 



