Minimum Essential Medium (MEM) with Earle′s Balanced Salts was developed by Harry Eagle as a result of his studies to determine the essential nutritional requirements of mouse L cells and HeLa cells in culture. He demonstrated that these cells require 13 amino acids and seven vitamins to grow and reproduce in vitro . MEM is a modification of Eagle′s earlier medium Basal Medium Eagle (BME), containing higher concentrations of the essential nutrients. These media have demonstrated the ability to support a variety of normal and transformed cells in culture and contain Earle′s Balanced Salts, which make them suitable for use in atmospheres charged with CO₂.