DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 27 



THIRTIETH-DAY STAGE. (S 11-4). 



In the cleared rib of the thirtieth day the fracture is well healed. The perios- 

 teum shows none of the thickening of the earlier stages. Some swelling due to 

 callus is evident at the site of the fracture. There are no staining features of 

 interest. In the cleared tibia, too, the bone ends are held together by firm callus. 



The cleared skull of the thirtieth day has stained but poorly. Trabeculae of 

 callus radiate from the site of the injury. Macrophages are noted within the spaces 

 of the callus, but are not numerous anywhere else. 



The sections of the long bone of this specimen show that there is little trace of 

 the original injury in the soft parts except the abundant scar tissue. As in the last- 

 mentioned stages, macrophages are present in larger numbers than normal in some 

 regions near the bone, often among scattered and small muscle-fibers. They are 

 comparatively small and pale-staining, and are the survivors from earlier and more 

 active periods. 



The callus of the thirtieth day is very extensive. In texture it is considerably 

 coarser than that of the twentieth day, the trabeculae being stouter and the spaces 

 larger. The area close to the original bone is occupied principally by marrow- tissue. 

 Farther out there is more bone, and the spaces are smaller. Large, thin-walled 

 blood-sinuses are frequent here, and around their walls are great numbers of reti- 

 culum macrophages. On the whole, however, the macrophages are much less 

 numerous and striking than at the twentieth day. The principal change in the 

 callus seems to be a strengthening of the permanent trabeculae, with a paring away, 

 here and there, of the temporary bone. 



FIFTY-FIRST (S 17-1), FIFTY-EIGHTH (S 15-1), AND FIFTY-NINTH (S 12-3) DAY STAGES. 



The cleared ribs of the fifty-first day show an almost normal contour, there 

 being hardly any swelling due to callus and the medullary cavity being quite 

 patent. Some blue staining is present around the site of the fracture, but this is 

 referable to the diffuse staining of the thickened periosteum and scar-tissue at this 

 point. The same faint diffuse blue appears in the fibrous membrane joining the 

 insert to the edge of the trephine opening in the cleared skull at this stage and is 

 also present in the fifty-eighth and fifty-ninth day skulls (foot-note, page 8, c). 

 There are no macrophages to be discerned in the cleared specimens of these periods. 

 In the sections of the fifty-first and fifty-ninth days the staining of the soft parts 

 presents nothing of interest. 



The callus of the fifty-first day is very compact and thick and can hardly be 

 distinguished from the original bone. Much of the space has been taken up by the 

 new, compact bone. The surviving trabeculae are stout and inclose large spaces 

 containing marrow-tissue. There are in this tissue comparatively few dye- 

 containing cells, and these are relatively small and weakly stained, resembling the 

 macrophages of ordinary marrow. It is evident from the appearance of the bone 

 that little or no osseous resorption is going on. A few giant-cells, containing no 

 dye-granules, are found in the marrow-tissue. 



