A Study of Thymic Lymphosarcoma Developing in Magnesium-deficient Rats¹ Free

A study of the incidence and fine structure of thymic tumors developing in magnesium-deficient rats has been done in 9 different experiments performed during the past three and a half years. Random-bred Sprague-Dawley and Wistar male rats, 6–7 weeks old, were used. Nineteen tumors were found among 92 rats sacrificed after an average of 65.2 days of deficiency. All the tumors can be classified as malignant lymphoma or lymphosarcoma and developed initially in the thymus. They produced metastases and lymphatic leukemia in some cases. A study of the ultrastructure of the normal thymus, the tumor, and the zone of invasion of the normal-appearing tissue by the tumor produced evidence of changes in both lymphocytes and reticular cells. Along the zone of invasion the lymphocytes contained large nucleoli, and the tumor cells showed a distinct lack of adhesion to one another. An increased number of free ribosomes and occasional colonies of intravesicular, virus-like circular particles were seen in the large lymphocytes of the tumor. These and other complex inclusions in the developing tumor are compared with circular or rod like intravesicular inclusions of the normal thymic reticular cell.