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  Table of Contents  
Year : 2013  |  Volume : 31  |  Issue : 2  |  Page : 201-203

How to liven-up an overhead projector presentation!

Department of Microbiology, Sree Balaji Medical College and Hospital, Chrompet, Chennai, Tamil Nadu, India

Date of Submission02-Dec-2012
Date of Acceptance24-May-2013
Date of Web Publication19-Jul-2013

Correspondence Address:
R Praveena
Department of Microbiology, Sree Balaji Medical College and Hospital, Chrompet, Chennai, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0255-0857.115239

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How to cite this article:
Praveena R. How to liven-up an overhead projector presentation!. Indian J Med Microbiol 2013;31:201-3

How to cite this URL:
Praveena R. How to liven-up an overhead projector presentation!. Indian J Med Microbiol [serial online] 2013 [cited 2020 Nov 28];31:201-3. Available from:

Dear Editor,

Computers have made "PowerPoint presentations" the preferred tool for large group teaching. Literature on student preferences on method of teaching favour visual aids for better understanding. [1],[2] The lacklustre overhead projector (OHP) is on the verge of being archived but for teaching centres at most developing nations and less resource regions of developed countries.

OHP can be used innovatively to perform animations - using what are called overlays (pieces of OHP sheets which can be placed over another large OHP sheet to produce superimposed image). This article deals with few new ideas to facilitate understanding of scientific concepts using an OHP presentation with "gram stain" as theme. Readers can modify the concept to suit their scientific content.

Gram staining separates bacteria into two broad groups (gram-positive and gram-negative).

The clinical specimen (e.g., pus, sputum, etc.,) is made into a smear on the microscope slide and is heat fixed. The staining procedure is explained in four steps.

The OHP sheet functioning as the base is placed on platen of the OHP projector [Figure 1]. Appropriate overlays are used to show the various steps [Figure 2] and [Figure 3].
Figure 1: Overhead projector sheet illustrating the microscope slide with smear and unstained bacterial cells as seen under microscope within the circle functions as the base

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Figure 2: Overlays 1-4 – small pieces of overhead projector sheets with the four reagents used in gram staining

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Figure 3: Overlays 5-8 used to explain the changes in colour bacterial cells undergo during staining process

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[Figure 4] explains step 1. Overlay 1 is placed on the base sheet and moved as if pouring the dye on the slide. This gives an animation effect. Overlay 5 is placed on the base sheet with the purple coloured cells over the unstained ones within the circle. This depicts all bacteria taking up the dye methyl violet to appear violet in colour.
Figure 4: Overlay 1 and 5 is placed on base sheet to explain step 1

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After removing overlay 1, step 2 is demonstrated by tilting overlay 2 over the slide [not shown in Figure]. Overlay 5 is retained on the base sheet. All bacteria remain violet after using grams iodine. Once the procedure is explained, all overlays are removed.

Step 3 is shown by placing overlays 3 and 6 on the base sheet [Figure 5]. Acetone acting as decolourising agent is explained. Overlays 3 and 6 are removed. Overlay 7 is kept to elucidate the spherical gram-positive cells alone retaining violet colour [Figure 6].
Figure 5: Overlay 3 and 6 illustrate rod-shaped gram negative bacteria losing colour when acetone is used

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Figure 6: Overlay 7 used to describe spherical gram positive bacteria alone retaining violet colour at the end of decolourisation

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Step 4 is executed by overlay 4 and superimposing overlays 7 and 8 to show the complete effect [Figure 7]. Decolourised gram negative cells take up dye dilute carbol fuchsin to appear pink, while gram positive cells remain violet. The circle shows the microscopic appearance of bacteria at end of staining procedure.
Figure 7: Overlay 4 is tilted to show staining. Superimposing overlays 7 and 8 displays fi nal microscopic picture when gram positive and gram negative cells are coloured violet and pink respectively

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Imaginative use of overlays, OHP/fabric paints, spirit-soaked cotton, sand or shadow art on OHP sheets can make complicated, multi-step procedures simple, clear and interesting with the choice of returning to a previous step for elucidation easily.

This makes OHP aided didactic lectures visually dynamic not to the extent of a PowerPoint presentation, but somewhere close to it. It opens up the scope for introducing active animations in OHP presentation, an element which is assumed to be absent in this method of lecture.

 ~ References Top

1.McCann AL, Schneiderman ED, Hinton RJ. E-teaching and learning preferences of dental and dental hygiene students. J Dent Educ 2010;74:65-78.  Back to cited text no. 1
2.Breckler J, Joun D, Ngo H. Learning styles of physiology students interested in the health professions. Adv Physiol Educ 2009;33:30-6.  Back to cited text no. 2


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]


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