THE DEVELOPMENT AND FUNCTION OF MACROPHAGES IN THE 



REPAIR OF EXPERIMENTAL BONE-WOUNDS IN RATS 



VITALLY STAINED WITH TRYPAN-BLUE, 



BY CHARLES CLIFFORD MACKLIN. 



INTRODUCTION. 



The vital-staining route as an approach to the problem of bone-repair came as 

 a natural consequence of the recent work of Shipley and Maoklin (1916 1 - 2 ) on osteo- 

 genesis. By subjecting very young, growing animals to trypan-blue, one of the 

 azo-dyes belonging to the benzidine series of colors, these investigators were able to 

 show that the regions of active bone-growth took a more intense stain than the 

 remainder of the bone; and, furthermore, that the heightened coloration was largely 

 referable to the presence in these areas of innumerable phagocytic cells, within whose 

 cytoplasm the dyestuff was stored in multitudinous tiny segregations known as 

 "dye-granules." 



These phagocytes were identified as the reticulo-endothelial cells of the young 

 bone-marrow. Their reaction to the dyestuff s of the benzidine group is the same 

 as that of the host of cells found throughout the body, which have been extensively 

 studied by different authors, and to which various names have been given, such 

 as "pyrrhol-cells" (Goldmann, 1909), "clasmatocytes" (Ranvier, 1899-1900), 

 "resting-wandering cells" (Maximow, 1906), etc. Recently Evans (1915) has 

 employed Metschnikoff's term "macrophage" to cover this entire group of phago- 

 cytic cells which are united by a uniform functional response to these colloidal 

 dyestuffs, and it is now well recognized that the term "macrophage" is a physiological 

 designation, including within its compass very diverse morphological elements. This 

 similar staining reaction, indeed, is but an expression of the phagocytic potentiality 

 which these cells hold in common (Evans and Schulemann, 1914) and which mani- 

 fests itself during their every-day existence in the ingestion and storage of certain 

 elements of the surrounding tissue-fluids. 



In consideration of the vigorous phagocytic properties attributed to these 

 cells, and also of their being present in large numbers where temporary bone and 

 cartilage were being absorbed, it seemed evident to Shipley and Maeklin (1916 2 ) that 

 they were a very important factor in active osseous development and that their 

 peculiar role under these circumstances was played in connection with the resorp- 

 tion of the provisional cartilage and bone. 



Now bone-resorption is an active process in the later stages of bone-repair, 

 for it is well known that the excess of provisional callus which is built up following 

 a bone-injury, such as a fracture, is gradually removed. Since the resorption of 

 this provisional callus is quite similar to that of provisional new bone it was decided 

 to investigate the vitally stained cells in the callus of healing bone-wounds and to 

 compare the findings with those in young, growing bone. 



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