This simple exercise is designed to allow students to explore the fundamental steps of the scientific method and at the same time reinforce basic microbiological laboratory techniques (wet mount, Gram staining, streak plating) and concepts (cellular versus colonial morphology). Each student is supplied with a nutrient broth culture containing at least two morphologically similar types of bacteria (e.g., Escherichia coli and Pseudomonas aeruginosa). After preliminary microscopic examinations of the organisms' cellular morphology (wet mount, Gram stain), the student is asked to hypothesize whether the "culture is pure" and subsequently perform an experiment to confirm this hypothesis (streak plate—colonial morphology).