In 1951, Harry Eagle determined thirteen amino acids minimally required to sustain the growth of most mammalian cells in culture. This led to his creation of the Minimal Essential Medium (MEM) now widely used for cultivating a wide variety of mammalian cell types in monolayer or suspension. The original recipe includes 29 components: 13 amino acids including glutamine, 8 vitamins, 6 salts, glucose, and additional serum protein as a supplement. However, depending on the application, numerous different commercial MEM formulations are available, such as low-serum, serum-free, with or without glutamine, and with or without phenol red.