Antibiotics are chemicals produced by one microbe that inhibit other microbes. Students study the effect of 6 different antibiotics on a Gram-positive bacterium and a Gram-negative bacterium. Exercise requires 2 consecutive days to complete. The Classroom Kit is designed for a class of 30 students; the Demonstration Kit is for individual use by the teacher or a student. With instructions. Each kit contains a coupon for the prepaid delivery of perishable materials. Return the coupon at least 2 weeks prior to the requested delivery date to ensure prompt arrival of materials.