"He Never Cleaned His Teeth" – van Leeuwenhoek's Discovery of the Oral Bacteria (1683)
 (A Great Moment in Microscopy reconstructed by Donald Cronkite and Jewel Reuter)

Antoni van Leeuwenhoek was a "draper," a merchant who sold cloth.  His all-consuming hobby was making microscopes and using them to look at practically everything.  Once he ignited gunpowder while watching it under a microscope.  Another time he tried to find out what made pepper hot.  One day he met an old man who said he had never cleaned his teeth.  This was the sort of thing van Leeuwenhoek lived for!  He scraped a sample from the teeth, put the material on a microscope, and saw.... "little animalcules," tiny creatures who were swimming and tumbling before his very eyes.  van Leeuwenhoek had already seen these animalcules in the water he soaked the pepper in, and now he was beginning to see how widespread they were.  Following up on this observation, he also looked at the teeth of women who cleaned their teeth daily -- and he saw the very same bacteria in that case.   

You Can Repeat Van Leeuwenhoek's Observation

 1.  Use a flat tooth pick to scrape gently on the region between the teeth.  Do not use a round, pointed toothpick and do not scrape on the gums and make them bleed.  All you need is some of the material in the groove between teeth.

2.  Put the material on a clean microscope slide and add a small drop of water.  Put on a cover slip.

3.  Find a place on the slide where you can see a mass of  material in a clump.  Look around the edges of such clumps for tiny particles that are moving in various directions.  There is a distinct difference between those particles that are actually swimming and those merely in Brownian motion.  You can see them better using a 40X (high dry) objective with moderate light.  But Leeuwenhoek would have used a lower magnification, no higher, probably, than 200 - 250 X. A 40X objective with a 10X eye piece would be 400X.

 Further activities

1.      Do different people have different numbers of "little animalcules?"  How can you count them accurately?
2.     Have a few students brush their teeth every day while a few students don't brush their teeth.  Then take a look.  Do you see more bacteria on one group's teeth?
3.    Get a copy of  Antoni van Leeuwenhoek and His Little Animals by Clifford Dobel and read about what van Leeuwenhoek saw in his own words.  A reprint of the  book is published by Dover Books.
4.  Do some research to find out more about plaque and plaque bacteria.
5.  Get some "disclosing tablets" from your dentist.  When chewed, these tablets show where you have not cleaned your teeth with a red (removable) stain..  What parts of your teeth do you miss when brushing? 

Donald Cronkite, Hope College, Holland, MI  49423  cronkite@hope.edu Jewel Reuter, Louisiana Virtual Classroom, New Orleans, LA 7001  jewelreuter@earthlink.net