"From a purely medical perspective, the thymus gland is like a 'nursery' for immune cells. Undifferentiated immune cells are 'born' elsewhere in the body (eg. white bone marrow), and then spend some time in the 'thymus nursery' where they grow and develop into very specific types of immune cells with their own specific functions. Once they've 'grown up', they are sent out into the body to 'do their job'."