Expert: Walter Hintz - 1/12/2009

Question
Dear Mr. Hintz, I'm a stay home mom knows very little about science.  My 6 years old started a science club few months ago with his best friends in school. Every two weeks all 9 kids meet at our house to learn different aspect of science.  Since his school doesn't allow time for kids to wash their hands washing before lunch (which drives me crazy), I thought it might be interesting to show the kids how dirty their hands are by the end of the day.  If there any experiments you can recommend?  Please advise.  Sincerly, Ying

Answer
Hi Ying Lee
The best way would be to culture the bacteria from the hands.  To do this you will need some media to grow them.  First check with a local hospital or biology department at a college and explain the problem.  Ask them if they will give you a petri dish or two with nutrient agar.  If not you will have to make some. Get some Knox gelatin and a beef bouillon cube. Dissolve the gelatin as directed and add the beef cube.  Poor the gelatin into small custard cups and let it gel.  Swap the boys hands with a cotton and swab the surface of the gel.  Keep in a warm place for a day or two.  Look for bacteria colonies.  Do not touch the colonies