I.] YEAST. 7 



sugar and keep it in a warm place : as soon as the mixture 

 begins to froth up, and the yeast is manifestly increasing in 

 quantity, it is leady for examination. 



A. MORPHOLOGY. 



1. Spread a little out, on a slide, in a drop of the fluid, 

 and examine it with a low power (J inch objective, 

 Hartnack, No. 4) without a cover-glass. Note the 

 varying size of the cells, and their union into groups. 



2. Cover a similar specimen with a thin glass and 

 examine it under a high power (^ objective. Hart- 

 nack, No. 7 or 8, Oc. 3 or 4). 



a. Note the size (measure), shape, surface and mode 

 of union of the cells. 



b. Their structure : sac, protoplasm, vacuole. 

 a. Sac ; homogeneous, transparent. 



/3. Protoplasm; less transparent; often with a few 



clear shining dots in it. 



y. Vacuole; sometimes absent ; size, position. 

 3. The relative proportion of sac, protoplasm, and 



vacuole in various cells. 

 Draw a few cells carefully to scale. 



3. Run in magenta solution under the cover-glass. (This 

 is readily done by placing a drop of magenta so- 

 lution in contact with one side of the cover-glass, 

 and a small strip of blotting paper at the opposite 

 side.) 



a. Note what cells stain soonest and most deeply, 

 and what part of each cell it is that stains : the sac 

 is unaffected ; the protoplasm stained ; the vacuole 

 unstained, though it frequently appears pinkish, 

 being seen through a coloured layer of protoplasm. 



