YEAST. w 7 



and, for this purpose, I did not make use of the compound juices of fruits, the 

 rigorous analysis of which is perhaps, impossible, but made choice of sugar, 

 which is easily analyzed, and the nature of which I have already explained. 

 This substance is a true vegetable oxide, with two bases, composed of hydrogen 

 and carbon, brought to the state of an oxide by means of a certain proportion 

 of oxygen ; and these three elements are combined in such a way that a very 

 slight force is sufficient to destroy the equilibrium of their connection. 



After giving the details of his analysis of sugar and of the products 

 of fermentation, Lavoisier continues : 



The effect of the vinous fermentation upon sugar is thus reduced to the 

 mere separation of its elements into two portions : one part is oxygenated at 

 the expense of the other, so as to form carbonic acid ; while the other part, 

 being disoxygenated in favor of the latter, is converted into the combustible 

 substance called alkohol ; therefore, if it were possible to reunite alkohol and 

 carbonic acid together, we ought to form sugar. 1 



Thus Lavoisier thought he had demonstrated that the carbonic acid 

 and the alcohol which are produced by the process of fermentation, are 

 equal in weight to the sugar which disappears ; but the application of 

 the more refined methods of modern chemistry to the investigation of 

 the products of fermentation by Pasteur, in 1SG0, proved that this is 

 not exactly true, and that there is a deficit of from 5 to 1 per cent, of 

 the sugar which is not covered by the alcohol and carbonic acid evolved. 

 The greater part of this deficit is accounted for by the discovery of two 

 substances, glycerine and succinic acid, of the existence of which La- 

 voisier was unaware, in the fermented liquid. But about 1^ per cent, 

 still remains to be made good. According to Pasteur, it has been ap- 

 propriated by the yeast, but the fact that such appropriation takes 

 place cannot be said to be actually proved. 



However this may be, there can be no doubt that the constituent 

 elements of fully 98 per cent, of the sugar which has vanished during 

 fermentation have simply undergone rearrangement ; like the soldiers 

 of a brigade, who at the word of command divide themselves into the 

 independent regiments to which they belong. The brigade is sugar, 

 the regiments are carbonic acid, succinic acid, alcohol, and glycerine. 



From the time of Fabroni, onward, it has been admitted that the 

 agent by which this surprising rearrangement of the particles of the 

 sugar is effected is the yeast. But the first thoroughly conclusive evi- 

 dence of the necessity of yeast for the fermentation of sugar was fur- 

 nished by Appert, whose method of preserving perishable articles of 

 food excited so much attention in France at the besnnnin^ of this cen- 

 tury. Gay-Lussac, in his " Memoire sur la Fermentation," 2 alludes to 

 Appert's method of preserving beer-wort unfermented for an indefinite 



1 " Elements of Chemistry." By M. Lavoisier. Translated by Robert Kerr. Second 

 edition, 1*79.3 (pp. 186-196). 

 5 "Annales de Chimie," 1810. 

 37 



