36 DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 



The morphology of these degenerate cells has been described in the text 

 (sixth-day stage). It appears that many (probably most) of the phagocytes fall 

 to pieces, their liquefied content of ingested material (which is assumed to be 

 changed in character) being returned to the lymph-spaces, from which it is passed 

 on to the blood-stream, to be excreted or utilized; and any fragments which remain 

 are probably devoured by the tissue-phagocytes. 



A few macrophages, however, as has been noted, persist on the field after 

 absorbable material has disappeared. In the fractures of the long bones these were 

 observed in numbers more or less above normal as far as the thirtieth day. They 

 haunt the surviving muscle-fibers and new scar-tissue. Their size and staining 

 ability gradually diminish, and they are quite inferior in these respects to the active 

 phagocytes; their numbers soon fall away to normal. 



It is difficult to say, from the evidence, whether or not these cells ever become 

 transformed into fibroblasts, as Goldmann (1912), Maximow (1902, 1906), and 

 Tschaschin (1913) suggest. The typical fibroblasts plainly are quite different from 

 the typical macrophages, and it seems probable that most, if not all, of the scar-tissue 

 arises independently of the macrophages. In the fifth-day stage, for instance, when 

 there is no perceptible diminution in the number of macrophages, there is much new 

 fibrous material. They, however, give place to scar- tissue, and, in a sense, may 

 be said to prepare the way for the scar by assisting in the removal of waste material 

 (Maximow, 1902). 



INTRAOSSEOUS MACROPHAGES. 



The second outstanding fact brought to light by the study of vitally stained, 

 healing bone-wounds is that the reticulo-endothelial cells of the callus-spaces 

 develop marked phagocytic power coincidently with the appearance of the erosive 

 processes concerned in the enlargement of these spaces; the intensity of this power, 

 too, seems to be roughly proportional to the amount of the callus breakdown. 

 There is, indeed, a most obvious parallelism in the curves tracing the degree 

 of activity of callus destruction, on the one hand, and the degree of phagocytic 

 efficiency of the macrophagic reticulum-tissue on the other, which is consistently 

 maintained throughout the entire history of the callus. 



From a review of the findings in the callus up to the sixtieth day it is possible 

 to divide the life of its macrophagic tissue, like that in the degenerate soft parts, 

 into the three phases: development, activity, and decline. Although these phases 

 merge gradually into one another, yet arbitrary limits may be set for them, that 

 of development covering the first nine days, that of activity, roughly, the period from 

 the tenth to the twentieth day inclusive, and that of decline the remaining time. 

 Having made this division, it is a simple matter to recount the most important 

 features of each phase. 



DEVELOPMENT. 



Upon referring to the records it will be noted that the callus rapidly develops, 

 following its first indication on the second day, and by the sixth day is quite well 

 marked. In this callus, spaces filled with cells (which are derived apparently from 



