IX.] YEAST. 385 



8. The relative proportion of cell- wall, 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 cell- 

 wall is unaffected; the protoplasm stained; the 

 vacuole unstained, though it frequently appears 

 pinkish, being seen through a coloured layer of 

 protoplasm. 



4. Burst the stained cells by placing a few folds of 

 blotting-paper on the surface of the cover-glass and 

 pressing smartly with the handle of a mounted 

 needle : note the torn empty and colourless, but 

 solid and uncrushed transparent cell-walls ; the soft 

 crushed stained protoplasm. 



5. Repeat observation 3, running in iodine solution 

 instead of magenta. The protoplasm stains brown ; 

 the rest of the cell remains unstained. Note the 

 absence of any blue coloration; starch is therefore 

 not present. 



6. Treat another specimen with potash solution, running 

 it in as before : this reagent dissolves out the proto- 

 plasm, leaving the cell-wall unaltered. 



M. 25 



