DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 23 



Since the macrophages are largest, most phagocytic, and most numerous where 

 resorption of the provisional callus is going on most rapidly, it is quite evident that 

 they are concerned very intimately with the clearing away of the callus. 



A thickening of the trabeculse which escape erosion is evident, and thus there 

 have been going on, side by side, the antagonistic processes of bone-erosion and 

 bone-building. 



Giant-cells are sometimes found, but contain no dyestuff. Large areas of 

 cartilage are seen in this specimen. Marrow tissue is present in some of the spaces. 



In the callus spaces of the skull macrophages are found, as in the callus of the 

 long bones. 



Passing in review the twelfth-day stage, there is to be noted an almost com- 

 plete cessation of tissue destruction, and the extraosseous macrophages are but 

 little increased over the normal. The callus, on the other hand, shows an exalta- 

 tion in staining and increase in size on the part of the macrophagic inhabitants of 

 the areas where bone destruction is actively proceeding. Bone-erosion and bone- 

 building are combining to give shape and strength to the permanent callus. 



THIRTEENTH-DAY STAGE. (S 11-3). 



The thirteenth-day stage shows essentially the same conditions. The staining 

 here is not good. In the cleared ribs no evidence of damaged tissue is present. 

 Macrophages are much reduced in number and staining intensity. Callus is well 

 advanced. 



In the cleared skull, owing to the poorness of the staining, neither stained 

 debris nor extraosseous macrophages can be made out. The callus is well marked 

 and a few blue-stained cells are seen in its spaces. 



FIFTEENTH-DAY STAGE. (S5-3). 



In the sections of the long bone of the fifteenth-day stage there is no diffusely 

 staining material to be seen. In the vicinity of the fracture, where tissue destruc- 

 tion has been proceeding, the muscle-tissue is loose, and the scattered fibers are 

 interspersed with scar tissue and macrophages. Transitional types are very rare. 

 No degenerate forms were noted, nor were any found in later stages. Scar tissue 

 is abundant. It seems to be evident that resorption of dead tissue has ceased. 

 The extraosseous staining presents a much less striking picture than in the earlier 

 stages, and from this period it becomes less and less noteworthy. 



The sections of the skull show no remaining dead tissue. It is not evident that 

 there is any excess of macrophages at the site of the healed wound. 



The callus of the long bones of S5-3 is quite extensive, but, judging from the 

 almost entire absence of typical osteoblastic formations on the periphery, its expan- 

 sion has practically ceased. The regions near the original bone are characterized 

 by thickened osseous trabeculse, often inclosing large tracts of loose cellular marrow 

 tissue, traversed by voluminous thin-walled blood-sinuses. Some macrophages 

 are found here, but in regions where the marrow tissue has become well established 



