In this lab (Activity #2 on page), learners compare bacteria growth on two petri dishes containing nutrient agar. Learners touch the doors, faucets, etc. in bathroom and then immerse their hands in 100 ml sterile water. They place 0.5 ml of this "dirty" water into one petri dish. They repeat this process again but wash their hands before immersing them in 100 ml sterile water. Learners incubate the plates for 24-48 hours and then score the results based on the bacteria growth they observe. Use this activity to emphasize the importance of hand-washing and the effectiveness of soap to disinfect.