Materials

• Microscope

• Square ocular grid

• Prepared slide of a blood smear

Procedure

1. Obtain an ocular grid etched with a square, and insert it into an ocular of the microscope (or use a microscope previously set up by the instructor).

2. Calibrate the ocular grid in a manner similar to that outlined in Exercise 3, and determine the area of each marked grid section. Draw the grid in the space below and add all pertinent dimensions.

3. Place a prepared slide of a blood smear on the microscope and focus on the slide using the 40X objective. Count the number of cells within the 4 margins of the grid area.

   Count only cells that touch the top and left margins of the grid. Do not count any cell that touches the right or bottom margin of the grid. Record the number in the following box.

4. Select 4 additional random fields of view with approximately the same density of cells and count the number of cells per grid. Record the numbers in the space provided.

5. Average the results and, based on the known dimensions of your grid, calculate the number of cells per mm ² for the blood smear.

   Area of the grid (40X) _____

   Cell Count	Number of cells/mm 2
   Average number of cells per mm 2 ____________