CHANGES IN THE AMOUNT OF MYELOCYTES IN THE THYMUS DURING ITS ACCIDENTAL INVOLUTION IN YOUNG RABBITS

In young rabbits, a quantitative study was made of the changes in the amount of myelocytes in the thymus during its accidental involution. As an agent to induce accidental ninvolution of the thymus an alarming dose of formalin was used. In was observed that with the progress of thymic involution, the cellularity of lymphocytes in the parenchyma became scanty, whereas thenumber of myelocytes per unit area of parendhma in sections ( here termed the concentration of myelocytes ) was considerably increased, so that not infrequently the histological picture of the thymic parenchyma was reminiscent of hypoplastic bone marrow. Even in such instances, however, the total amount of myelocytes per thymus did not increase, because the reduction in tha mass of thymic parenchyma took place to a greater extent. This implies that a high concentration of myelocytes of the thymus in an advanced satgeof involution in a result of condensation of there cells in the reduced parenchyma. The concentration of myelocytes in the parenchyma was reduced to the normal level coincident with the commencement of regenration of the thymic lymphocytes. Either in order lymphoid organs or in the liver and spleen, there appeared no foci of myelocytes throughout the experimental period. This research was conducted under the direction of Professor Bunsuke Osogoe. I wish to express my thanks to him for constant guidance in the course of the work.