In 1900, John Beard wrote “It has fallen to my lot to show that the first leukocytes arise in the thymus, from its epithelial cells, and that the thymus must be regarded as the parent source of all the lymphoid structures of the body…., so the original leukocytes, starting from their birth place in the thymus, have penetrated into almost every part of the body, and have created new centres for growth, for increase, and for useful work for themselves and for the body” Miller JFAP, Thymus 1:3-25, 1979