CHAPTER VI. 



Fermentation {^continued). 



Soluble Constituents of Yeast — Action of these upon Sugar— Conversion of 

 Glycogen in the Liver and other tissues— Growth of Yeast-Cellsin Organic 

 and Inorganic Fluids — Fermentation of Fruit Juice — JEtohKc and Anae- 

 robic Fermentations — Effect of Free Oxygen on Yeast-Cells — Fermen- 

 tation not necessarily equal toGrowth of Yeast — Enzyme or Unorganized 

 Ferment a Secondary Function — Function depends partly on Organism, 

 partly on Medium in which it is Growing — Peptonizing Function 

 usually requires presence of Oxygen — ^Various kinds of Fermentation : 

 Lactic, Urea, Butyric, Ammoniacal, Acetic — Formation of Fatty 

 Acids — Mycoderma Aceti— General Processes of Fermentation — 

 Hoppe-Seyler's Classification. 



On approaching the subject of fermentation by yeast we find 

 at the very outset that Pasteur and others had noticed a 

 very remarkable pecuUarity of the water in which yeast had 

 been mixed, and from which it had again been separated. 



It was observed that a certain substance, perfectly soluble in 

 water but precipitable by alcohol, had the peculiar property 

 of inverting saccharose into equal quantities of dextrose and 

 laevulose, and it was at once assumed that this invertin, 

 invertase, or some similar substance, produced through the 

 vital activity of the yeast-cells, was necessary to bring about 

 conversion of starch into sugar (diastase), or of saccharose into 

 invert sugar (invertin), before the cells could bring about a true 

 fermentation, or splitting up and hydration into alcohol 

 and carbonic acid gas, with certain other products to be 

 mentioned immediately. It was noticed by Bertholot and 

 Hoppe-Seyler, moreover, that, even if the living organisms 

 were first killed by the addition of ether, the invertase or 

 invertin still continued to act, and was able to invert a 

 quantity of saccharose altogether out of proportion to the 

 amount of inverting material present. In consequence of 

 the latter part of this observation, many physiologists and 

 chemists maintain that the action of the invertin is essenti- 

 ally due to the setting up of a certain rate and length of 



