Counting Tetrahymena with a Hemacytometer

Materials:

 * Hemacytometer


 * Tetrahymena cultures


 * Formaldehyde (FA)


 * 70% Ethanol

Method:

 * 1) Clean the chambers of the hemacytometer and cover slip with 70% ethanol.  Dry and gently fix the coverslip in position.
 * 2) Pipette 200 μL of Tetrahymena cells in a microcentrifuge tube. Add 2 μL of formaldehyde and mix by inverting 2-3 times.
 * 3) Add 10 μL of the fixed cells to each chamber depression. Do not overfill.
 * 4) Place the chamber in the compound microscope under a 10× objective and adjust the focus to distinguish the cells. Switch to a higher objective if need be.
 * 5) Count the cells in the large, central gridded square. The gridded square is circled in the graphic below. Multiply by 10,000 to estimate the number of cells per mL. Count the other grid and average the counts from the two grids.


 * Cells should be uniformly distributed (and not clump together) as it is assumed that the total volume in the chamber represents a random sample. 


 * Mix the cell suspension thoroughly before taking a sample to count as the sample will not be representative if the cells start settling before a sample is taken.