There are around 37 trillion cells in the human body. But those can be categorized into how many types? A simple Google search will yield a result of about 200, but some researchers, including Jay Shendure, a geneticist at the University of Washington, think that number is quite low. Therefore, Dr. Shendure has created a way to count the types of cells by measuring the activity of genes inside over 42,000 cells at once. How can this benefit the study of human health? Why does this matter?