Final answer:
John Snow did not contribute to the establishment of cell theory. His work focused on epidemiology, unlike that of Robert Hooke and Anton van Leeuwenhoek, who made direct contributions to cell theory.
Step-by-step explanation:
The individual who did not contribute to the establishment of cell theory is John Snow. Cell theory was developed in part due to the work of scientists like Robert Hooke, who coined the term "cell" when he observed cork tissue, and Anton van Leeuwenhoek, who first discovered bacteria and protozoa. Theodore Schwann, along with Matthias Schleiden, further contributed to cell theory by proposing that all living things are composed of cells. John Snow, however, is known for his work in epidemiology, specifically his study of cholera transmission, and did not contribute directly to the development of cell theory. Other significant contributors to cell theory include Rudolf Virchow, who famously stated omnis cellula e cellula, meaning that all cells come from existing cells.