Dr. Miller became expert in removing a mouse thymus, performing thymectomies. He wasn’t the first, but he took it to extreme lengths, trying all kinds of permutations. In a significant one, he took a mouse and gave it a leukemic filtrate at birth. After a short period of time, he took out the mouse’s mature thymus and replaced it with the thymus of a baby mouse. The mouse would promptly get leukemia. In fact, the adult mice contracted cancer at whatever point they got the immature thymus.
