DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 7 



There are, then, both within the shaft of the bone and in the tissues of its 

 immediate environment, under normal conditions, appreciable numbers of macro- 

 phages. In the next section it will be found that, following bone injury, their 

 numbers are locally very much increased. 



SECOND-DAY STAGE. 



The earliest stage of bone repair examined was that at the end of 2 days 

 (animalS 18-1). 



On inspection of the cleared ribs with the binocular microscope the most obvious 

 change, as compared with the control, is the marked blue staining of the broken 

 ends of bone and of the material surrounding them. The ends of the medullary 

 canal are plugged with it. This staining is shown in black* in figure 2. It is very 

 dense and irregular in character and quite different from the granular type of 

 staining presented in the control rib (fig. 1). The impression conveyed is that 

 the tissue injured by the trauma, and the associated exudate, have absorbed the 

 dye. There is as yet very little swelling at the site of the fracture, so that the 

 contour of the bone, apart from the distortion of the break, is the same as that of 

 the control. 



Under the highest power of the binocular the blue granules, representing 

 macrophages, are seen, as in the control, in the periosteum and marrow cavity of 

 the bone, and in the surrounding connective tissue. At the site of the fracture, 

 however, it is noted that they are more numerous than elsewhere and they have 

 apparently been increased in this region. In the drawing (fig. 2) they appear 

 as a small cloud of granules near the broken bone-ends and around the densely 

 colored material. This granular appearance is a true intra- vital dyeing, and 

 stands in sharp contrast to the diffuse and dense staining above described. The 

 periosteum as yet shows no obvious changes, such as thickening. 



In the cleared skull, as in the ribs, a dense and diffuse blue staining is seen in 

 the bone fragments and in other dead tissue resulting from the operation. Macro- 

 phages are not definitely increased. 



In the cleared long bones the tissues of the fracture-precinct are densely stained, 

 but the specimen, on account of its thickness and opacity, is unsatisfactory for 

 inspection of the macro phage tissue. 



As would be expected from the cleared specimens, the uncounterstained 

 sections of long bone (tibia) show areas near the broken ends where the misshapen 

 and apparently injured tissue has taken a dense, irregular, and diffuse blue stain. 

 Under higher powers such areas appear as shapeless blue masses of fragmented 

 muscle-fibers, a little fibrous tissue, blood, and invading phagocytes, interspersed 

 with clearer areas of exudate. Often individual muscle-fibers appear stained blue 

 throughout. There is evidently much cell liquefaction going on. 



Diffuse staining of this type is an indication of cell death (MacCurdy and 



*All blue staining is represented diagrammaticallv in the illustrations by the denser black. 



