Medium 199 was developed specifically for nutritional research of chicken fibroblasts. Today, 199 media are widely used for the maintenance of non transformed cells, vaccine and virus production and primary explants of epithelial cells. The media formulated with the Hanks salts are buffered with saline solutions designed for balancing in ambient conditions, and their use in a CO₂ incubator results in a rapid drop in pH of the culture medium.