By loading toxins of S. typhi, S. paratyphi A, B, and E. coli to the bone-marrow tissue culture of normal rabbits as well as loading toxins of E. coli and S. typhi to the bone-marrow tissue culture of normal persons, the author studied the influences of these toxins on the tissue growth; and also by adding the toxins of the same bacilli to the bone-marrow tissue culture of normal rabbits in fluid medium, pursued the influences on the increasing rate of erythrocyte count and hemoglobin content. Further, by loading the serum of patient with typhoid fever to th bone-marrow tissue culture of normal rabbits the author observed the influences of the serum on the tissue growth, and obtained the following results. 1. The toxins of S. typhi and S. paratyphi A and B both possess the action inhibiting the leucopoetic functions of the rabbit bone marrow to the greatest degree, while the toxin of E. coli shows hardly any effect. Moreover, the influences of the toxins of S. typhi and E. coli on the bone-marrow tissue of normal persons are exactly identical with those against the bone marrow of normal rabbits. From these results it is assumed that a direct action of the toxins of S. typhi disturbing the bone-marrow functions plays an important role in causing the leukopenia in typhoid fever. 2. It has been recognized that in the serum of the serum of the patient with typhoid fever there exist factors that directly inhibit the growth of the normal rabbit bone marrow tissue. 3. The direct action of these toxins on the erythrocytes and hemoglobin content in the normal rabbit bone marrow is not so significant. Therefore, the iron-retention in the reticuloendothelial system and another secondary reaction, which are the commonly accepted theory, seem to play a leading role for the anemia in typhoid fever.