DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 35 



loidal dyestuffs (Evans and Schulemann, 1914). The ultramicrons of such dyestuffs 

 in some way permeate the cell-membrane and are combined in aggregations which 

 soon become visible by the aid of the higher powers of magnification as multi- 

 tudinous, isolated granules. It appears, too, that often an aggregation of dye- 

 molecules is situated within a vacuole in the cytoplasm. This fact has led some 

 workers to suppose that the cell was attempting to subject the material so housed 

 to a form of digestion in which it would be made useful, or at least harmless, and 

 that its treatment of this colloidal dyestuff was an example of its behavior toward 

 any material in the same physical condition. 



The same reasoning may be applied to the interpretation of the behavior of 

 the macrophages in fractures, and we may postulate that the colloidal waste 

 products resulting from the breakdown of the tissue are similarly acted upon within 

 the cell economy. This may be a productive mechanism. It is a well-known fact 

 that certain of the products of protein-splitting, if generally scattered throughout 

 the circulation, will bring about great harm. Now it is quite possible that some at 

 least of the products of proteolysis in fractures and other wounds are of this noxious 

 character, and it may well be that the macrophages are called out to form a barrier 

 against the escape of these materials into the general circulation. There is a stasis 

 of fluids in these regions, and thus the conditions are most favorable for phago- 

 cytosis (Downey, 1917). Indeed, in emergencies such as the healing of wounds and 

 clearing away of damaged tissue resulting from gross insults, the macrophages may 

 be considered as expressing in an exaggerated form the same function they express 

 every day under normal routine conditions of metabolism as in the breaking-down 

 of red blood-cells, or it may be of the protoplasm of muscle-fibers. Here it is note- 

 worthy that Goldmann (1909) finds these cells especially numerous in the heart a 

 hard-worked muscular organ. Not all tissues, however, are to be looked upon 

 as producing materials which are dealt with in this way; for instance, nerve-tissue 

 contains few or none of these cells (Goldmann, 1909), and hence the functional waste- 

 products of this tissue may be considered as being treated in some other manner. 



DECLINE. 



As to the fate of the macrophages of the inflammatory area, it has been noted 

 that, shortly after the disappearance of the tissue-waste, the macrophages, in all 

 the specimens, become less and less evident, finally dwindling to their normal 

 numbers (table 2). The examination of the sections throws some light on the final 

 end of the individual cells. As early as the third day we have noted that certain of 

 the phagocytes had a degenerate appearance, and these were more numerous on 

 the fifth day. It seems evident that some of the cells start to degenerate quite 

 early, even at the stage where new macrophages are developing and where the 

 macrophagic tissue is, on the whole, increasing. On the sixth day the degenerate 

 cells were present in enormous numbers, especially in the young scar- tissue, and it 

 is at this time that most of the phagocytes undergo dissolution. After the first week 

 they disappear more slowly, for but few degenerate forms are noted; indeed none 

 was seen after the twelfth day. 



