[Histological changes of the thymus in the aged].

Thymus tissues from 70 autopsy cases (aged 40-89 years) were examined. The thymic parenchyma decreased progressively corresponding with ageing and was replaced synchronously by the adipose tissue. Anyhow, the thymic tissue did not disappear completely, but became small irregular islands distributed dispersively in the fibroadipose tissue and lost its normal structure of thymic lobules and demarcation between cortex and medulla. Additionally, lymphocytes and Hassall's corpuscles were markedly decreased in number. In stress involution caused by chronic diseases, the thymic parenchyma presented further atrophic changes.