We have already shown that removal of the spleen (1) or of the thymus (2) has very little effect on the animal economy. Since the spleen and thymus together comprise the largest amount of lymphoid tissue in the body of young animals, it would appear not improbable that although removal of either of these organs causes no marked disturbance, their simultaneous extirpation might be expected to give rise to some more manifest change. Friedleben (3) states that, while in his series of experiments no dog died of removal of the thymus, and that the removal of the spleen in young dogs does not influence the course of life, the simultaneous removal of the thymus and spleen causes a marked deterioration of blood formation, and leads to death.