256 APPLIED BACTEEIOLOGY 



is modern, and is the outcome of a series of discoveries 

 principally due to Black, Lavoisier, Liebig, Schwann, and 

 latterly to Pasteur and Hansen. 



Sugar disappears during fermentation; but that is not 

 all. Carbonic acid gas is given off, and alcohol is formed. 

 Sugar contains carbon, hydrogen, and oxygen; so does 

 alcohol, but in other proportions. In carbon dioxide or 

 carbonic acid gas there is only carbon and oxygen. The 

 decomposition of sugar is, therefore, accompanied by a 

 complete breaking up. Fermentation consists, therefore, 

 in the breaking up of chemical compounds, the molecules 

 of which they are composed being torn apart from one 

 another, and then allowed to form simpler and more stable 

 compounds. Owing to the setting free of such energy as 

 has been stored up in such a highly complex substance as 

 sugar, which is no longer required to maintain the high 

 level of combination, a certain proportion is released in the 

 form of heat. This is why the temperature of a ferment- 

 ing liquid always rises without the addition of any external 

 heat. 



Thus, it is seen that the act of fermentation is commonly 

 the result of, or rather the accompaniment of; vital action. 

 In the presence of the Sacch. cerevisice or other yeast, 

 in saccharine liquids which contain small quantities of 

 phosphates and albuminoid matter, glucose is converted 

 into alcohol and carbonic acid gas, together with small 

 quantities of glycerine, succinic acid, etc. Yeast contains 

 also a soluble ferment which converts sucrose, or ordinary 

 cane-sugar, into glucose. Therefore cane-sugar, or sucrose, 

 may be converted into alcohol and carbonic acid gas, the 

 soluble ferment first converting the sucrose into glucose, 

 which then becomes decomposed by the action of the yeast. 

 The conversion of the glucose may be represented by the 

 following formula : 



