Final answer:
Friedrich Miescher's research on nucleic acids involved working with nucleated white blood cells extracted from used surgical bandages. These cells were preferable for studying the cell nucleus, leading to his discovery of what is now known as DNA.
Step-by-step explanation:
Friedrich Miescher worked with white blood cells (leukocytes) when he discovered nucleic acids. During his experiments, Miescher isolated the nuclei of leukocytes found in pus from used surgical bandages. These cells were ideal because they have a large nucleus compared to cytoplasm, which made it easier to study nuclei and their contents.
While red blood cells in humans do not contain nuclei and are primarily involved in the transport of respiratory gases, white blood cells are key components of the immune system and contain a nucleus where DNA is stored. Since Miescher was interested in the chemistry of the cell nucleus, the nucleated white blood cells were the cells of interest for his groundbreaking research that led to the identification of what he called nuclein, today known as DNA.