IX.] YEAST. 385 



S. 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. 



4. Burst the stained cells by placing a fe^y 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 sacs; 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 sac unaltered. 



7. [On staining with Haematoxylin-ammonia, one or more 

 bodies may be distinguished by their deeper colour, 

 which are probably of a nuclear nature.] 



M. 25 



