Part IV: Measuring Quantities Using Ocular Lenses and Counting Chambers Measuring Quantities Using Ocular Lenses and Counting Chambers Measuring Techniques D4

Preface: Before beginning this module, you should be familiar with the parts, use, and care of the compound microscope. Before beginning this module, you should be familiar with the parts, use, and care of the compound microscope. If you are unsure about the microscope’s operation, please review the Use of the Microscope module. If you are unsure about the microscope’s operation, please review the Use of the Microscope module.Use of the MicroscopeUse of the Microscope Mishandling of the microscope can lead to damage of the instrument. Mishandling of the microscope can lead to damage of the instrument.

Notes During microscopic observations, it is sometimes necessary to find out the number of organisms in the sample. Consequently, a variety of measuring and counting ocular disks have been developed to make the task easier and more accurate. An ocular disk is designed for use within the ocular lens. To insert a disk simply remove the lens assembly from the ocular, insert your lens, then replace the assembly.

Cross-hair disc The Cross-hair disc divides the field of vision into four quadrants and is used for counting relatively larger specimens.

Finder disc The Finder disc is numbered 1 through 5 from the center of the disc out. The numbers are used as indicators when one person would like to call another person’s attention to a particular part of the field of view.

Net disc The Net disc is a 5.0 mm square divided into either 1.0 or 0.5 mm squares. It is frequently used for counting large materials, like coarse abrasives.

Whipple disc The Whipple disc is a square subdivided into 4 smaller squares on each slide. Each of theses is further subdivided into 25 smaller squares. This is used in counting bacteria and dust particles.

B. Measuring Quantities Using Counting Chambers At various times you might be required to count the number of organisms in a given volume of liquid. This type of count is usually associated with bacteriological or medical testing. A variety of counting chambers are designed to give accurate counts of cells or organisms under various conditions. A variety of counting chambers are designed to give accurate counts of cells or organisms under various conditions.

Hemacytometer Counting Chamber This device has 2 separate cell counting areas, each containing 0.1 cubic mm of sample when covered by a cover slip.

Two Counting Chambers are formed using a Special Cover Slip 3. A special cover slip mounts on two ground glass bars to form the top of the two chambers. Bar

Transfer Cell Suspension to each Chamber by Capillary Action  Fill each chamber with cell suspension using a fine tip glass pipet applied to the beveled area of each chamber.  Allow suspension to be drawn into the chamber by capillary action.  Do Not force the filling with pressure.

Counting Grids Fine rulings on the floor of each chamber provide grids to help count the number of cells in suspensions of blood cells or other cell types. The # cells per ml = average cell # per large square x 10 4.

Howard Mold Counting Chamber 4. The Howard Mold Counting Chamber is specifically designed for counting the number of mold and yeast particles in a given volume of food. 5. The structure of the chamber is similar to that of one side of the hemacytometer, but there are no grid markings on the chamber floor. 6. A Howard ocular disc in the eyepiece of the microscope is used instead to facilitate counting.

Howard Mold Counting Chamber

Sedgewick-Rafter Counting Cell The Sedgewick-Rafter Counting Cell consists of a brass or polystyrene rectangular frame bonded to a heavy glass slide. Covering the cell with a flat cover glass creates a 1 ml counting chamber commonly used in limnology laboratories to determine the number of plankton in a 1 ml sample of water.

Module Completed! Please return to the main desk to obtain a post test from your friendly Science Learning Center personnel. Please return to the main desk to obtain a post test from your friendly Science Learning Center personnel.