Have individuals wash their hands with soap and water, give one of them a yeast-covered piece of candy, and then have him shake hands with the person next to him. Handshakes continue down the line until everyone in the class has had contact. You will follow by swabbing each participant's hand to start a culture. As a result, the class will discover how easily and how far down the line the yeast "disease" spread. This is a terrific class project for studying communicable disease.