FERMENT A TION ai i 



alcohol (Udranski, 1889), we have obviously to do with a special kind of 



metabolism whose significance is unknown but which has nothing to do 



with alcoholic fermentation (Wortmann, 1898). Into the question of the 



occurrence of other secondary products, such as aldehyde, volatile acids, &c., 



we need not enter ; these are doubtless formed also in pure yeast fermentations, 



but they are not actually products of fermentation. There are also other 



bodies present which give definite characters to the fermented liquor, but 



these are not due specially to the yeast but to the fermentable material ; in the 



case of wine they are derived from the grape. 



The decomposition of sugar into alcohol and carbon-dioxide is remarkably 



complete ; this is best seen by a comparison of the structure of (i-glucose with 



the products of fermentation : — 



OH OH H OH OH H^OH H3 H3 Hg H^ 



I I I I I I II II 



C— C — C — C — C — C = C— C + CO3 + CO2 + C — c 



I I I I I I 



H OH H H OH OH 



It has not hitherto been possible to carry out this decomposition by purely 

 chemical means, and hence it was for long thought that the living protoplasm 

 alone had the power to bring it about. Recently, however, E. Buchner (1897 

 onwards) has succeeded, by vigorous friction and under high pressure, in obtain- 

 ing a sap from yeast, which can induce the formation of alcohol from all the 

 carbohydrates that the yeast acts on. Buchner' s view is that fermentation is 

 a purely chemical process, carried out by definite substances present in the 

 expressed sap. Buchner' s explanation has not remained unchallenged ; doubts 

 have been expressed in the first place whether the decomposition of the sugar 

 effected by the expressed sap is identical in character with that produced by the 

 living protoplasm, and, secondly, it has been suggested that the activity of the 

 expressed sap is due to living yeast protoplasm contained in it. If that be so, 

 yeast protoplasm must have certainly extraordinary powers of resistance, since 

 after precipitation with alcohol and acetone the redissolved precipitate still 

 retains its activity. Recently, Albert (1901) has met these objections by kill- 

 ing the yeast in alcohol and ether, when, notwithstanding this treatment, he 

 found that its power of fermentation was unaffected ; the dead cells were able 

 to form alcohol from sugar, whether in the natural or in the crushed state. 

 The fermentation in the former case is intra- cellular as in the case of living cells ; 

 the sugar is split up inside the cells, for the fermenting substance cannot pass 

 through the cell-wall. This, however, is not extraordinary, for it has been 

 established that many enzymes are incapable of passing through the cell-wall. 

 Buchner unhesitatingly considers this body as an enzyme and calls it 'zymase'. 

 It must, however, be remarked that zymase has not much in common with the 

 enzymes we have previously studied, for these act by relatively simple methods, 

 e. g. hydrolysis, a power possessed by inorganic agents also. In addition to 

 hydrolysing enzymes we have also oxidizing enzymes to take note of. Zymase 

 differs from all of these in being much more thorough in its action and in 

 possessing the power of breaking down the sugar molecule into new combina- 

 tions of carbon, hydrogen, and oxygen. [According to Buchner's (1905) 

 observations it would appear that lactic acid is not improbably an inter- 

 mediate product in alcoholic fermentation.] 



But zymase differs from hydrolytic enz5mies in another respect. The 

 duration of its activity at summer temperature is very slight ; it is very rapidly 

 destroyed, and in order to obtain large quantities of alcohol much expressed sap 

 and concentrated sugarsolutions mustbe employed, whilst in the case of ordinary 

 enzymes small amounts are able to produce great changes. This distinction 

 may not, however, be of great importance since it is possible that the activity 

 of zymase may be inhibited by the enzymes in the expressed sap ; still the 



