NUTRITION OF YEASTS. 227 



Molisch found that small quantities of iron exert a favour- 

 able influence on the propagation of pressed yeast. Kos- 

 sowicz showed, moreover, that in this respect ferrous sulphate 

 has a much more favourable effect than ferric chloride. 



With regard to the importance of carbon compounds for 

 the nutrition of yeast, Laurent, in particular, proved that 

 yeast can assimilate, in addition to sugar, large quantities of 

 such compounds as lactic acid, glycerine, dextrin, tartaric 

 acid, etc., but not oxalic acid and its potassium and ammonium 

 salts. In practice, sugars play the chief part in nutrition, but 

 the species of yeast differ amongst themselves in this respect, 

 as well as in their power of fermenting these carbohydrates. 

 Thus, according to Beijerinck, Schizosaccharomyces octosporus 

 can readily assimilate maltose, glucose, and Isevulose, but not 

 saccharose and lactose. 



Glycogen constitutes an essential part of the cell contents 

 at a certain stage of its life. This is specially the case when 

 the liquid is rich in carbohydrates, which are stored up as 

 reserve material in this form. Glycogen was discovered by 

 Errera in yeast, and has been more closely studied by other 

 investigators. Laurent proved that yeast can store up very 

 considerable quantities. It appears in the cell as minute 

 semi-fluid drops, with no definite form, and gives a reddish- 

 violet coloration with iodine, which disappears on warming. 

 When the food supply shows signs of becoming exhausted, 

 the yeast cell falls back upon its glycogen. 



With regard to possible sources of nitrogen for yeast, it may 

 iirst be noted that amongst inorganic sources the ammonium 

 salts are readily absorbed. It was proved by Pasteur that yeast 

 can grow in a nutritive fluid containing no organic nitrogen, 

 but only nitrogen in the form of ammonium tartrate (100 c.c. 

 water, 10 grammes sugar, 0-1 gramme ammonium tartrate, 

 and the ash from 1 gramme of yeast). Subsequently Willdiers 



Hanson's artificial culture fluid contained 

 88'5 grammes distilled water. 

 0*2 gramme magnesium sulphate. 

 0*3 .. monopotassium phosphate. 

 1-0 peptone (Witte). 

 10*0 grammes saccharose. 



