Camillo Golgi studied the central nervous system during the late nineteenth and early twentieth centuries in Italy, and he developed a staining technique to visualize brain cells. Called the black reaction, Golgi’s staining technique enabled him to see the cellular structure of brain cells, called neurons, with much greater precision. Golgi also used the black reaction to identify structures within animal cells like the internal reticular apparatus that stores, packs, and modifies proteins, later named the Golgi apparatus in his honor. Golgi, along with Santiago Ramón y Cajal, received the Nobel Peace Prize in 1906 for their independent work on the structure of the nervous system. Golgi’s discovery of the black reaction enabled other scientists to better study the structure of the nervous system and its development.

Heinrich Hermann Robert Koch was a researcher from Germany who studied the causative agents of infectious diseases in various parts of Europe, Africa, and Asia during the late nineteenth and early twentieth centuries. Koch developed what researchers call Koch’s postulates, which are four criteria designed to establish whether a bacterium causes a certain disease, and as of 2025, many researchers still use Koch’s postulates to guide their research. He also received the Nobel Prize in Physiology or Medicine for his discovery of Mycobacterium tuberculosis, which is the bacterium responsible for tuberculosis, an infectious disease that primarily attacks the lungs. Koch’s research on identifying disease-causing bacteria for various infectious diseases has advanced disease prevention and treatment, especially for tuberculosis, which has the ability to transmit from mother to child.