DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 43 



after the debris has been cleared up, is what would be expected, since so little of the 

 insert is eroded. 



A note may here be made as to the condition of the healing areas of skin over 

 the trephined bones. Several of these were cleared and some were sectioned. It 

 was found that macrophages are increased in certain places, especially around the 

 suture holes, in the earlier stages. This was noticed in the skulls of the following 

 days: second (S 18-1), ninth (S 17-2), tenth (S 5-1), and twentieth (S 12-2). Thus 

 the macrophages appear to have a function to perform in the solution of the sutures 

 and probably in the repulsion of infection as well. In the actual scar-tissue the 

 trypanophil phagocytes are few in number. It is of interest to observe that Gold- 

 mann (1912, p. 80) noted a similar increase of macrophages in healing skin wounds 

 of the rat. 



CONCLUSIONS. 



The following conclusions are based solely upon investigations with the rat. 

 It seems probable, however, that they would hold good in general principle for the 

 other mammals, and no doubt for many of the lower forms. 



In the healing of bone-wounds, macrophages, which stain brilliantly with 

 trypan-blue, soon congregate at the site of the injury and become very numerous, 

 hypertrophied, and of increased phagocytic power. They assist in dealing with the 

 tissue-waste resulting from the trauma. These phagocytes are developed prin- 

 cipally from the lymphocyte-like cells from the blood-stream, but also from local 

 mononuclear cells with phagocytic potentialities. Most of them ultimately dis- 

 integrate in situ. 



During the structural changes attending the transformation of provisional 

 into permanent callus, trypanophilic macrophages develop in the callus-spaces from 

 the reticulum cells and become numerous, large, and phagocytic. They function 

 in the removal of redundant bony spicules, their particular role being con- 

 cerned with the absorption of the waste products from the breaking down of the 

 matrix. When cartilage is present in the callus they also play a part in its removal. 

 Their action here is thus the same as that of the macrophages of developing bone. 



The macrophages of soft parts and bone, though morphologically different, 

 are physiologically similar. They phagocytize the products of proteolysis and 

 segregate the material within their cytoplasm, where they probably subject it to a 

 form of digestion. 



Limited numbers of polymorphonuclear leucocytes were encountered among 

 trypanophilic macrophages in areas undergoing repair. No dye-granules were 

 found in them. Physiologically they are distinct from the macrophages. 



The osteoclasts of the callus did not show dye-granules. Their numbers did 

 not bear any relation to the apparent amount of bone-destruction which was going 

 on. Osteoblasts, too, contained no dye-granules. 



