SACCHAROMYCES 393 



plums, cherries and other fruits. The cells are usually 

 elliptical in outline, but elongated forms are frequent. 



The ascospores, 2 to 4 ,a in diameter, are produced in 

 about twenty hours at 25 C. 



Like the above species it does not ferment lactose. 



(iv) S. flava lactis, Kruger. This form produces 

 yellow colonies with rapid liquefaction on gelatine media : 

 it was originally isolated from a " cheesy " butter which 

 had a disagreeable odour of decomposing urine. Its 

 cells are ellipsoidal and about 4 ^ long. It ferments 

 lactose as well as maltose and cane-sugars. 



(v) Saccharomyces fragilis, Jorgensen, obtained from 

 Kefir, ferments milk-sugar with production of a small 

 quantity of alcohol. 



It is a small oval species, sometimes with elongated 

 cells : two to four oval ascospores are, produced in about 

 twenty hours when the cells are grown on gypsum 

 blocks at 25 C. 



Ex. 174. Obtain a small piece of German yeast. Break it 

 in pieces and stir it up in water in a tea-cup. Allow the yeast 

 to settle and pour off the water. Mount in water a drop of the 

 creamy yeast left at the bottom of the cup, and examine with a 

 high power. 



Draw a single cell and observe its cell-wall, protoplasm, and 

 vacuoles. 



Ex. 175. Half fill a small tea-cup with water and dissolve in it 

 a teaspoonful of sugar, put in a piece of German yeast about the 

 size of a broad-bean and stand the whole in a warm place. 

 When the yeast begins to accumulate on the surface of the water, 

 take a very minute portion and mount it in water. Examine 

 with a high power and sketch the budding or sprouting 

 cells. 



Ex. 176. Smear some of the creamy yeast from Ex. 174 on 



