588 VITAL ACTIONS OF THE LOWER FUNGI. 



A. Alcoholic Fermentation of Suyar by Yeast. 



Fermentesci- The fermentescible material is furnished by the 

 le material. g i ucoseg of the f ormu i a C 6 H 12 6 , namely, dextrose, 



Isevulose, lactose, or galactose ; further, by maltose, to 

 which the formula C 18 H 34 17 is given, and which, there- 

 fore, only acquires the same composition as glucose by 

 taking up water. Dextrose forms the most favourable 

 material ; if it is exposed to fermentative action in a 

 mixture along with other forms of glucose, for example, 

 laevulose, the dextrose is the first to undergo fermenta- 

 tion. Cane-sugar and milk-sugar only undergo fermen- 

 tation when they are converted into glucose ; the former 

 can be converted into dextrose and laevulose by means 

 of invertin (therefore by yeast), the latter is transformed 

 into galactose and dextrose by means of a ferment pro- 

 duced by some fungi ; further, they can both be converted 

 into these glucoses by boiling with dilute mineral acids. 

 Other carbo-hydrates also, such as starch, gum, and 

 cellulose, can be converted into glucose by ferments, or 

 by treatment with acids ; starch is transformed into 

 dextrose by means of ptyalin and also by acids, and into 

 maltose by diastase (malt). All the carbo-hydrates last 

 mentioned can therefore, in like manner, serve for fer- 

 mentation, if only ferments which transform them into 

 glucose are at the same time present in the fermenting 

 mixture ; and as these ferments are usually produced in 

 large quantities by the same organisms which cause the 

 fermentation (invertin by yeast, the ferment which trans- 

 forms milk-sugar by bacteria), the incapacity of cane- 

 sugar, starch, &c., to undergo fermentation directly is 

 practically of little account, and fermentation frequently 

 occurs when these substances are present, and when the 

 directly fermentescible glucoses are absent, being at 

 most somewhat delayed in its commencement. By 

 being provided with ferments which form glucose, the 

 area of the vital and fermentative activity of the fer- 

 mentative agents is markedly enlarged. 



Forms of The specific decomposition of glucose into alcohol 



yeast capable an( j carbonic acid is limited to yeast, but all the species 



of exciting * 



fermentation, of saccharomyces are not able to set up an equally 



