ALCOHOLIC FERMENTATION 81 



of its reserve products, absorbing oxygen and giving off carbon dioxide. 

 Yeasts are also able to take oxygen from compounds in which it is 

 loosely combined. It is thus, as Schutzemberger and Risler have 

 stated, that when fresh yeast is placed in arterial blood or in a solu- 

 tion of hemoglobin saturated with oxygen, the color passes from a 

 deep red to a bluish black. In this case the yeasts take their oxygen 

 from the blood and act like tissue cells in the animal body. While 

 yeasts are able to take oxygen only from such unstable combinations 

 as hemoglobin, they are not able to get it from compounds which 

 hold it firmly. For instance, they are without action on indigo carmin 

 which some bacteria decolorize so strongly. 



The respiratory activity measured by the oxygen consumed in a 

 unit time by a unit weight of yeast, varies with the temperature. 

 It is very feeble at 10, increases slowly up to 18, and attains its 

 maximum towards 60. It falls quickly after the death of the yeast. 

 The experiments of Grehant and Quinquand have given the same re- 

 sults. They have shown that respiration diminishes a little and re- 

 duces itself to a minimum during the anaerobic life of the yeast, 

 but never totally disappears. As has been stated before, Griiss re- 

 garded glycogen as important in respiration. According to this au- 

 thor, glycogen is a reserve product utilized in respiration and fermen- 

 tation.- It is by means of their oxidases that yeasts oxidize the glucose 

 secured by hydrolysis of glycogen, transforming it into carbon clioxide 

 and water. 



ALCOHOLIC FERMENTATION 



General Characteristics of Alcoholic Fermentation 



Conditions Necessary for Its Production 



While the molds produce very quickly on the surface of liquids 

 a vigorous vegetation, and thus live in contact with air, the greater 

 number of the yeasts develop at the bottom of culture media in the 

 form of a sediment, and it is only under exceptional circumstances 

 that they develop on the surface in the form of a pellicle often 

 called a scum. 



When cultivated in a dish containing sugar solution in a thin 

 layer, the supply of air is sufficient to allow a vigorous growth of 

 the yeast. Under these circumstances, it decomposes the sugar, 

 using part for maintaining protoplasm or constructing new substance, 

 and transforming the rest by oxidation to carbon dioxide and water. 

 In a word, it is aerobic and acts like other plants. 



The activities are different when it is put into a flask almost 

 completely filled with a sugar solution and to which air does not 



