RECENT STUDIES have demonstrated that the thymus is essential in newborn rodents for development of immunological competence1 and for induction of lymphatic leukemia.2 The ultrastructure of normal mouse thymus has been studied by Clark3 and by Weiss4 and the ultrastructure of fetal hamster thymus by Weakley et al.5 Others have examined thymus of mice with virusinduced leukemia6 and have reported numerous virus particles at the surfaces of lymphocytes, in the intercellular spaces, and in phagocytes. However, De-Harven7 has described virus-like particles in thymus of normal Swiss mice.
In conjunction with electron microscopic studies of human leukemic thymus, the thymus glands of 20 human fetuses were examined to provide information concerning their ultrastructure and to determine whether virus-like particles could be identified.
Materials and Methods
Thymus glands were obtained at postmortem examination from 20 liveborn human fetuses resulting from spontaneous abortions or premature