The Autonomous Behaviour of Normal Thymus Grafts

SUMMARY The growth of individual thymus grafts in isologous mice was unaffected by the presence of as many as twenty‐three other thymus grafts in the same host animal. The lymphoid organs of mice bearing multiple thymus grafts showed little deviation from normal. Thymus fragments, as small as 0·5 mg., were successfully grafted, but all successful grafts contained medullary tissue. The percentage of medullary tissue in all types of thymus grafts was constant and the size attained by a thymus graft appeared to be determined by the size of the surviving medullary tissue from the original graft.