The exercise is introduced with a discussion of observations that were made in the early nineteenth century. Namely, that biological stains often show specific affinity for particular subcellular components. With this information, students use differential staining procedures to identify nuclear and cytoplasmic components in cells from thymus and onion root tip. In the second part of the exercise, cell nuclei are isolated from thymus tissue and their purity assessed by staining techniques. The DNA is isolated from the nuclei by a procedure designed to provide information on the packaging of this macromolecule in the chromosome. The exercise gives students experience with both classical and contemporary techniques, and makes them aware that cell and molecular biology have long histories that can be traced to traditional disciplines.