12 DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 



that it does not undergo cytoplasmic hypertrophy; indeed, the only noticeable 

 change in it is the usual increase in tabulation of the nucleus, this structure being 

 quite complex at times. 



The presence of these neutrophiles in an area of inflammation, even of the 

 aseptic type, which we have here to deal with, is of course to be looked for, and it 

 may be that one of their functions here is the elaboration of proteolytic enzymes; 

 more commonly they are found closely associated with the disappearing tissue than 

 in the open spaces. 



Fibroblasts were fairly abundant throughout the wound-area. In some of 

 these a few fine round dye-granules were observed; the most, however, appeared 

 unstained. 



The skull sections show substantially the same picture as the long bones. 

 There is a good deal of fragmented and pulped debris which stains diffusely and 

 densely blue, thus confirming the findings for this specimen in the gross cleared 

 condition. This material is the bone dust and other tissue injured in the operation. 

 There is also quite a lot of extravasated blood and exudate. Though macrophages 

 were not discerned in the cleared specimen, in the sections they are very numerous, 

 but the picture is hardly as striking as in the long bones. Transitional types of 

 dye-containing cells are seen, as in the long bones, but are less abundant. Distinct 

 staining of the ends of the cut bone is present. Polymorphonuclear leucocytes are 

 fairly numerous, but contain no dye, even where they appear among the densely 

 staining debris. 



On the third day the sections, like the cleared ribs, show the callus somewhat 

 thicker and more vascular than on the second day. It is particularly well seen in 

 the sections of the long bones. There is much more ossification evident than here- 

 tofore, and distinct trabeculse, staining like bone and containing definite bone-cells, 

 project into the outer, more cellular layer. Somewhat larger spaces, with osteo- 

 blasts lining their walls here and there, occur between the trabeculse. Many of 

 these contain capillaries of small caliber. The largest spaces are situated close to 

 the original bone. Often it is evident that they communicate with the Haversian 

 canals of the bone, which have apparently undergone an enlargement in the regions 

 close to the callus. Frequently such a space is found to contain a blood-sinus, and 

 in some spaces there may be situated a multinucleated basophilic cell resembling 

 a mass of osteoblasts. These cells are probably the so-called "osteoclasts." They 

 are not numerous, and no dye-granules were found in them. 



When the cleared and uncounterstained section is looked at with the low- 

 power the callus has a pale-bluish appearance with a few spots of darker blue 

 representing scattered cells. Under the oil immersion these cells are found to 

 occupy the interstices between the young bony plates; they are reticular cells, and 

 in them it is possible, by close scrutiny, to see a very faint blue granulation. They 

 are to be regarded as the young recruits of the army of macrophages which will 

 inhabit the expanding callus spaces in the later stages. They are largest and their 

 granulation is most marked in areas near the original bone indeed here, especially 



