14 DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 



appeared, which are as yet, for the most part, not strongly stained; to these an 

 important phagoeytic role is assigned. * 



FIFTH-DAY STAGE. (S 12-1). 



On the fifth day the cleared preparation of fractured ribs shows the macro- 

 phagic sheath still very conspicuous about the area of the wound, its blue lines of 

 trypanophil cells stretching out into the muscle and invading the spaces between 

 the fibers. Within it the clear zone of young callus is somewhat increased. The 

 staining of the ends of the bones is less marked, and it is probable that this is 

 because the dead material is being cleared away; there is also less blue debris 

 around the bone. Large macrophages are seen about the ends of the bone and in 

 the entrances of the marrow cavity. The macrophages are at least as numerous 

 as on the third day and are distinctly larger in size, being quite conspicuous even 

 under the low power of the binocular. 



In the sections of the long bones hosts of macrophages throng the areas of effete 

 muscle and other tissue damaged by the trauma. Diffusely staining damaged 

 tissue is found, but is somewhat less marked. There is a slight amount of extra- 

 vasated blood and fluid exudate. The macrophages are very large and are loaded 

 with dye-granules. There are not so many transitional types as in the third-day 

 stage. They resemble in form those already described. The exhausted or involu- 

 tion forms, seen now and then in the third-day stage, are here somewhat more 

 often found; as before, they are much more frequently encountered in scarring 

 areas. In some the cytoplasm presents nothing more than a mere network in 

 which an occasional dye-granule is seen. 



Some of the cells show a very few large granular masses, suggesting that 

 the smaller dye-granules have coalesced; occasionally a macrophage is encoun- 

 tered in which the nucleus stains diffusely, thus pointing to the death of the cell 

 (MacCurdy and Evans, 1912). These results may be due to an overloading of the 

 cell with dyestuff. Sometimes, too, diffuse staining of cell inclusions leads to such 

 optical effects. Similar cell-staining has been described by other authors, as 

 Tschaschin (1913). 



Polymorphonuclear leucocytes are not so numerous as on the third day. They 

 were not found to contain dye-granules, although this animal was subjected to the 

 vital dye for 72 hours. 



Scar formation is in progress, and the fibroblasts are of a more mature type. 

 Rarely indeed are dye-granules, even of small size, to be found in them. 



In the skull sections of the fifth-day stage there is still some damaged tissue, 

 taking a diffuse blue stain. The ends of the bone are tinged, but rather less strongly 

 than before. Dead fibers of muscle and connective tissue stain bluish and show 

 stained nuclei. There is some extravasated blood and fluid exudate. 



In association with this debris, macrophages are abundant, but are not so 

 marked as in the long bones. As in the long bones of this stage, there are compara- 

 tively few transitional types. 



