Thymus (source code)
= Thymus
The <thymus> is an <organ> of the <lymphatic system> involved in development of <T cells>. In humans it lies in the chest behind the <sternum>. Its anatomical position and its contribution to <immunity> are different properties: locating an <organ> does not by itself reveal its function.<Thymus in the NCI Dictionary of Cancer Terms>[Definition: lymphatic organ, T lymphocytes and position behind the breastbone]{ref}
A motivating experiment removed the <thymus> from newborn mice. In his firsthand account, <Jacques Miller> describes finding a deficiency of <lymphocytes> in other lymphoid tissues and failure to reject foreign <skin grafts>. Supplying circulating <lymphocytes> or a thymus graft could restore the graft-rejection response. Removal, a functional test and rescue together connected the <thymus> with development of immune competence.<Professor Jacques Miller, pathologist in Conversations with Australian scientists>[Why did the mice waste away? An unexpected finding: lymphocyte deficiency, graft acceptance and rescue]{ref}
A further comparison separated two consequences. In germ-free conditions, mice subjected to neonatal <thymectomy> could remain healthy yet still fail to reject <skin grafts>. Thus wasting illness and the measured graft-rejection defect were not interchangeable observations.<Professor Jacques Miller, pathologist in Conversations with Australian scientists>[So why did the mice waste away?: germ-free mice and retained graft-acceptance phenotype]{ref}
For an original experimental-design outline, compare sham-operated and thymectomized animals under matched conditions, then score <lymphocyte> abundance, health and graft rejection separately. Include a defined rescue condition. These endpoints distinguish loss of immune competence from a nonspecific effect of surgery. The neonatal timing matters: an experiment on development does not justify assuming that removal at every age has identical effects.
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