132 



is not at once boiled and is left exposed to the air, the process 

 known as fermentation rapidly sets in and that if this is 

 allowed to continue we ultimately obtain in place of the sugar 

 solution one which contains alcohol, carbon dioxide gas being 

 evolved during the process. Yeast Fungi are therefore of 

 great commercial importance in the manufacture of wine 

 from the sugar in grapes, in the preparation of spirit from the 

 sweet-tasting mahua (Bassia latifolia) flowers and in the manu- 

 facture of wine, beer and spirits, generally. If the minute oval, 

 or spherical, cells of a Yeast Fungus are placed in a suitable 

 nutrient sugar solution they are found to grow and multiply 

 with great rapidity, the peculiar method of multiplication 

 being termed budding. The cell wall of the Yeast Plant 

 bulges out and a protuberance is formed which gradually 

 increases in size, the neck connecting it with the mother-celt 

 remaining narrow. A cell- wall is then formed across the 

 narrow neck at the point of union and the swollen protu- 

 berance, separating from the mother-cell, becomes a separate 

 cell which then behaves in the same way. When all the sugar 

 has become converted into alcohol and the food material is 

 consequently exhausted, the yeast cells can no longer continue 

 growing and budding and they proceed to form spores. The 

 protoplasm in each cell divides into four little blocks, each 

 block becoming a spore, which is eventually set free by the 

 disintegration of the wall of the mother-cell. Under favour- 

 able conditions each of these spores germinates and at once 

 proceeds to grow and bud off new cells as described. 

 Ferment It has been noted above that bacteria are capable 



Q f causm g various kinds of fermentation but they do not 

 produce the alcoholic fermentation so characteristic of the 

 Yeasts. Plants, such as bacteria and fungi, which are able 

 to produce fermentation are known as Ferment Organisms 

 (sometimes also as Organised Ferments). Such plants appear 

 to owe their power of producing fermentation mainly to the 

 chemical substances known as Enzymes which they contain r 

 and which, of course, are not living organisms. The action 

 of the Yeast on the sugar solution will be understood from 

 the following equation : 



(grape sugar) (alcohol) (carbon dioxide) 



and it should be noted that, although the Yeast derives its 

 food f-rom the sugar, yet only a very small proportion of the 

 solution is actually utilised as food, the remainder being 



