Part IV:Part IV: Measuring Quantities Using Ocular Lenses and Measuring Quantities Using Ocular Lenses and

Counting ChambersCounting Chambers

Measuring TechniquesD4

Preface: Before beginning this module, you should Before beginning this module, you should

be familiar with the parts, use, and care of be familiar with the parts, use, and care of the compound microscope.the compound microscope.

If you are unsure about the microscope’s If you are unsure about the microscope’s operation, please review the operation, please review the Use of the Use of the MicroscopeMicroscope module. module.

Mishandling of the microscope can lead to Mishandling of the microscope can lead to damage of the instrument.damage of the instrument.

NotesDuring microscopic observations, it is sometimes During microscopic observations, it is sometimes necessary to find out the number of organisms in the necessary to find out the number of organisms in the sample. Consequently, a variety of measuring and sample. Consequently, a variety of measuring and counting ocular disks have been developed to make the counting ocular disks have been developed to make the task easier and more accurate.task easier and more accurate.

An ocular disk is designed An ocular disk is designed for use within the ocular for use within the ocular lens. To insert a disk lens. To insert a disk simply remove the lens simply remove the lens assembly from the ocular, assembly from the ocular, insert your lens, then insert your lens, then replace the assembly.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 At various times you might be required to count the number of organisms in a given count the number of organisms in a given volume of liquid. This type of count is volume of liquid. This type of count is usually associated with bacteriological or usually associated with bacteriological or medical testing.medical testing.

A variety of counting chambers are A variety of counting chambers are designed to give accurate counts of cells or designed to give accurate counts of cells or organisms under various conditions. organisms under various conditions.

Hemacytometer Counting Chamber

This device has 2 separate cell counting This device has 2 separate cell counting areas, each containing areas, each containing 0.1 cubic mm0.1 cubic mm of of sample when covered by a cover slip. sample when covered by a cover slip.

Two Counting Chambers are formed using a Special Cover Slip

3.3. A special A special cover slip cover slip mounts on two mounts on two ground glass ground glass bars to form bars to form the top of the the top of the two chambers.two chambers.

Bar

Bar

Transfer Cell Suspension to each Chamber by Capillary Action

Fill each chamber with Fill each chamber with cell suspension using a cell suspension using a fine tip glass pipet fine tip glass pipet applied to the beveled applied to the beveled area of each chamber.area of each chamber.

Allow suspension to be Allow suspension to be drawn into the chamber drawn into the chamber by capillary action. by capillary action.

Do Not force the filling Do Not force the filling with pressurewith pressure. .

Counting Grids

Fine rulings on the floorFine rulings on the floorof each chamber provideof each chamber providegrids to help count the grids to help count the number of cells in number of cells in suspensions of blood suspensions of blood cells or other cell types.cells or other cell types.

The # cells per ml =The # cells per ml =average cell # per average cell # per large square x 10large square x 1044..

Howard Mold Counting Chamber

4.4. The Howard Mold Counting Chamber is The Howard Mold Counting Chamber is specifically designed for counting the number specifically designed for counting the number of mold and yeast particles in a given volume of mold and yeast particles in a given volume of food.of food.

5.5. The structure of the chamber is similar to that The structure of the chamber is similar to that of one side of the hemacytometer, but there of one side of the hemacytometer, but there are no grid markings on the chamber floor. are no grid markings on the chamber floor.

6.6. A A Howard ocular discHoward ocular disc in the eyepiece of the in the eyepiece of the microscope is used instead to facilitate microscope is used instead to facilitate counting.counting.

Howard Mold Counting Chamber

Sedgewick-Rafter Counting CellThe Sedgewick-Rafter Counting The Sedgewick-Rafter Counting Cell consists Cell consists of a brass or polystyrene of a brass or polystyrene rectangular frame rectangular frame bonded to a heavy glass slide.bonded to a heavy glass slide.

Covering the cell with a flat Covering the cell with a flat cover glass creates cover glass creates a 1 ml counting chamber a 1 ml counting chamber commonly used in commonly used in limnology laboratories to limnology laboratories to determine the number determine the number of plankton in a 1 ml sample of of plankton in a 1 ml sample of water.water.

Module Completed!

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