DESCRIPTION OF FIGURES. 



B, original bone. M, macrophage. N, nerve. 



BS, blood-sinus. M<\ marrow-cavity. /', periosteum. 



C, callus. A/us., muscle. *>', scar-tissue. 



PLATE 1. 



FIG. 1. Portion of normal rib from rat vitally stained with trypan-blue. The black dots represent macrophages 



normally present in the marrow-cavity, periosteum, and tissue around the bone. X 27. This and the 



next five figures are free-hand drawings from gross cleared preparations under the binocular microscope. 



The macrophages are represented somewhat larger than they actually are, for the sake of plainness. 

 FIG. 2. Fractured rib of rat on second day of repair. Note the de'bris around the ends of bone and the slight increase 



in macrophages as compared with figure 1. X 27. 

 FIG. 3. Fractured rib of rat on third day of repair. Great increase in macrophages is seen, with swelling due to 



young callus. Diffusely stained debris present. X 27. 

 FIG. 4. Fractured rib of rat on ninth day of repair. Macrophages somewhat less numerous. Callus much more 



dense. X 27. 

 FIG. 5. Fractured rib of rat on twentieth day of repair. The contour of bone is almost normal, the medullary cavity 



is being restored, and macrophages are but little in excess over the normal. X 27. 



PLATE 2. 



FIG. 0. Trephined skull of rat on ninth day of repair. A bone-disk has been inserted on the left side, while the right 

 has been left open. Note the crowds of macrophages in the open spaces and around the bone edges. 

 Here and there are areas almost free from phagocytes; these are patches of scar tissue. Early callus 

 spicules line the bone edges. X 10. 



FIG. 7. Photomicrograph of area near broken end of long bone from rat on third day of repair. The edge of Lone 

 (B) and the fragments of dead tissue are stained blue. Myriads of macrophages (M) are found through- 

 out the figure. X 40. 



FIG. 8. A few cells selected from specimen from which figure 7 was made, showing the development of the large 

 macrophages from the small lymphocyte-like cells. As a rule, more and more dyestuff is taken up with 

 increase in size of the cell. Besides the dye the cells also contain the tissue-waste which they have 

 phagocytized. Free-hand drawing. X 1,000. 



PLATE 3. 



FIG. 9. Photomicrographs from a cleared and uncounterstained section of the sixth-day stage in fracture-repair. 

 Exactly the same field is seen in the two pictures, but that on the left received a much longer exposure, 

 so that practically the only objects seen in it are the macrophages. These are larger and more thickly 

 distributed in the central and lower right regions. Here the greatest amount of diffusely stained tissue- 

 waste is present, as is seen by the denser staining in this region in the right-hand picture. The field 

 is from an area of degenerating muscle. Above and to the right is scar-tissue (.S), while below and to 

 the left the muscle is beginning to deteriorate. In the central and lower right areas the muscle is degen- 

 erate, and here the macrophages (M) are largest and most numerous. X 50. 



FIG. 10. High-power drawing (camera lucida) of area of degenerating muscle from a region similar to that shown 

 in figure 9 (M). Fragmented muscle-fibers are seen, together with young fibroblasts, polymorphonu- 

 clear leucocytes, and macrophages. Three small lymphoeytoid cells appear. Some of the macro- 

 phages contain more blue dye than others; the latter are usually stuffed full of phagocytized material. 

 One small macrophage has engulfed a polymorph. X 1,000. 



FIG. 11. A few degenerate macrophages from an area of scar-tissue, similar to that shown in figure 9 (S). They are 

 of different sizes. Some appear vacuolate and ragged; others are mere fragments. They contain 

 comparatively little dye. Some young fibroblasts are shown. X 1,000. 



FIG. 12. A portion of a callus-space from the sixth-day stage. A thin-walled blood-sinus (B.S') is conspicuous, and 

 between its walls and the bone (C) are situated rcticulum cells, some of which contain dyestuff (M) 

 and are thus phagocytic. X 1,000. 



FIG. 13. Three reticulum phagocytes from the callus of the sixth-day stage, showing mitosis in dye-containing cells. 

 There are two metaphases and an anaphase. X 1,000. 



PLATE 4. 



FIG. 14. Old bone (B) and callus from the tibia of the tenth day. Camera-lucida drawing, from cleared section. 

 The spaces near the original bone are filled with the largest and brightest macrophages (M). Under 

 high magnification these large phagocytes are shown in figure 15 o. Here, too, there are blood-sinuses. 

 Farther out the macrophages are less conspicuous and are absent at the periphery. X 80. 



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