42 DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 



is sudden, vigorous, and of short duration, their period of maximum efficiency being 

 from the third to the sixth days inclusive; whereas the effort of the intraosseous 

 elements begins later, is more gradual in onset and less violent, and is of longer 

 duration, the period of maximum efficiency of these cells ranging from the tenth 

 to the twentieth days. Both types, however, are apparently stimulated to hyper- 

 trophy and functional efficiency by the same type of material waste resulting 

 from proteolysis; but the call is apparently much more sudden, forceful, and per- 

 emptory in the soft parts than in the callus, so that here an expeditionary force of 

 potential macrophages from distant regions must be rushed in. The needs of the 

 callus, on the other hand, in the matter of its resorption, are apparently served 

 adequately by the exaltation of the powers of the resident phagocytes. Both 

 macrophagic types are concerned in like manner in the treatment of dissolved 

 tissue-waste, and they are thus physiologically similar. In both types phagocytic 

 activity has been developed coincidently with the occurrence of tissue breakdown. 

 Both have a reconstructive as well as a scavenger function, for they prepare the 

 ground for scar-tissue or permanent callus, as the case may be. Most of the cells 

 of the soft parts perish in situ, while the fate of the callus-cells is obscure; no 

 involution forms, however, were found among them. 



Macrophages were found in healing wounds of membrane-bone, not only in the 

 surrounding soft parts but in the spaces of the callus itself. Here the cells were of 

 the reticulum type and were related to blood-sinuses as in the long bones. The 

 callus of membrane-bone was rather slower in development and was relatively 

 small in volume, so that the pictures presented by callus in the trephine-wounds 

 of the skull were not so striking and instructive as those in the long bones. They 

 were useful, however, in confirming the findings in the long bones. 



It is worthy of emphasis that the method of vital-staining, as applied to 

 developing callus on the one hand and to developing bone on the other, demonstrates 

 very forcibly that the same cellular elements are at work in the performance of a 

 like task. Macrophages of identical morphological type are found in mass forma- 

 tion in each case, intimately related to areas of bone or cartilage resorption, and for 

 them a common physiological significance is claimed that of phagocytizing the 

 products of disintegration of provisional cartilage and bone. More than this, 

 there was found absolutely no trace (in the osteoclasts of either callus or developing 

 bone) of any phagocytic activity. Thus the conclusions of Shipley and Macklin 

 (1916 2 ) in regard to developing bone are upheld by the findings in callus. 



From an examination of all the cleared and sectioned skulls it may be said 

 that no difference can be discerned in the staining reactions consequent upon 

 putting the insert back right side up, or upside down, or inserting living or dead 

 bone from another rat, or even foreign dead bone. Thus the macrophages, as far 

 as could be made out, behave alike toward all these types of insert. In no case was 

 the insert removed, although the edges were trimmed and rounded off; and, 

 although here and there in some of the older skulls there was some slight evidence 

 of erosion in the inserts and in the surrounding bony edges, it is remarkable how 

 little of the insert disappears. The absence of an increased macrophagic tissue, 



