PLATE 24.

FIG. I.-Tuberculosis of the Spleen. 92. Two tubercles are seen situated beneath the capsule: 1, Thickened fibrous capsule; 2, trabeculæ ; 3, caseated centers of the tubercles; 4, giant cells. FIG. II.-Central Portion of a Spleen-follicle in Diphtheria. X 745. There are seen numerous, large, polygonal cells with vesicular, swollen nuclei (1), some are filled with small, dark, nuclear fragments (2), also free chromatin granules (3).

THE BONE MARROW.

In the adult the bone-marrow is the principal seat of production of red corpuscles. The shafts and the distal epiphyses of the long bones contain the yellow, fatty marrow; all other bones, the red marrow. The red marrow consists of an extremely fine reticulum, in which the cellular elements and the vessels are suspended. Here are found, first of all, the so-called myelocytes, or marrow-cells, which are ameboid cells of the type of lymphocytes, but with larger, though less chromatic, nuclei ; 1; lymphocytes, such as are found in the blood; large protoplasmic cells with regularly fragmented, lobulated nuclei, or many nuclei,-the giant cells of the marrow, or mye

PLATE 25.

FIG. I.—Bone-marrow from the Diaphysis of the Humerus in Pernicious Anemia. × 520. The normal fat of the marrow has almost disappeared. At 1 only a few fat-cells or fat-vacuoles are seen; the number of cells in the marrow is greatly increased; 2, white marrow-cells, myelocytes; 3, the same with several nuclei ; 4, nucleated, red blood-corpuscles; 5, cells containing red blood-corpuscles; 6, eosinophilic cells; between the cells a fine fibrillar reticulum.

FIG. II.-Bone-marrow in Acute Leukemia from the Di= aphysis of the Femur. 640. The fat of the marrow has disappeared here also. 1, Erythrocytes; 2, myelocytes, greatly increased in number; 3, lymphocytes; between the cells is the reticulum.