In 1942, Merrill Chase discovered that cells taken from the peritoneum of Guinea pigs that had been immunized against an antigen could transfer immunity when injected into Guinea pigs that had never been exposed to the antigen; this phenomenon was the discovery of cell-mediated immunity. Subsequent research attempted to uncover how the cells imparted their effects. Henry Sherwood Lawrence, in 1955, discovered that partial immunity could be transferred even when the immune cells had undergone lysis - indicating that cells did not need to be fully intact in order to produce immune effects. Lawrence went on to discover that only the factors less than 8000 Daltons were required to transfer this immunity; he termed these to be "transfer factors".