76 PHYSIOLOGY OF YEASTS . 



is best adapted to yeast metabolism. This sugar is assimilated by 

 practically all of the yeasts. Dextrine is transformed by certain 

 varieties (Mycoderma and Torula), but is not well adapted to others. 

 Sucrose which is so easily fermented does not play any role in as- 

 similation. The same is true with regard to glucose, levulose, raffi- 

 nose, and arabinose. Finally, lactose is not assimilated except in 

 isolated cases. Lindner, 1 in a later publication, stated that maltose 

 is easily available as a nutrient sugar, glucose, fructose, and cane sugar 

 being less valuable. In fact sucrose was often valueless. 



On the other hand, the experiments of these authors have showed 

 that there is no relation between the fermentability of a sugar and its 

 use as an nutrient. Thus it is that one frequently meets yeasts 

 which, in functioning aerobically, energetically assimilate a sugar, 

 while, functioning anaerobically, they are unable to ferment it. One 

 may encounter, although rarely, a yeast which is able to ferment a 

 sugar and not able to use it as a nutrient. Such is the case with 

 S. Ludwigii, exiguus, cartilaginosus and Sch. Pombe and mellacei 

 which produce an active fermentation of glucose, levulose and sac- 

 charose but are unable to assimilate any of them. 



Kluyver 2 attributed the statements that yeast is able to assimilate 

 maltose to the fact that the maltose contained glucose. When the 

 maltose was purified and freed from the glucose no assimilation was 

 secured. Lindner 3 has shown that maltose is easily assimilated by 

 yeasts. Glucose, sucrose, and fructose were less satisfactory. 



It is known since the work of Errera that glycogen is abundant 

 in yeast cells. Since it is there so abundantly, it seems to have con- 

 siderable importance in the life of the yeasts. The study of the con- 

 ditions for its formation is very interesting and may explain many 

 facts with regard to the hydrocarbon nutrition of yeasts. This study 

 has been made by Laurent who has stated that glycogen is able to 

 be formed at the expense of the following substances: 



Lactates 



Succinic acid and ammonium succinate 



Malic acid and malates 



Mannite 



Sugars of the C 6 Hi 2 O 6 and Ci 2 H 2 2On series 



Glycogen 



1 Lindner, P. The results obtained in fermentation and assimilation experi- 

 ments with yeasts. Chem. Ztg. 34, 1144. Chem. Absts. 6 (1912) 1050. 



2 Kluyver, A. J. Assimilability of maltose by yeasts. Biochem. Zeit. 52, 

 486-493. 



3 Lindner, P. The results obtained in fermentation and assimilation experi- 

 ments with yeasts. Chem. Ztg. 34, 1144. 



