. Modern surgery, general and operative. matory exudate enters into the blood-clot and theleukocytes eat up and destroy the clot. The clot is simply dead materialand in no way contributes to repair. The cells of the damaged tissue pro-liferate and the young proliferating cells (fibroblasts) enter into the spaces inthe clot which were eaten out by the leukocytes. Finally, the entire clot isreplaced by fibroblasts and much of this cellular mass quickly becomes vas-cularized (granulation tissue). The osteoblasts which exist in the deeper layers of the periosteum and,in the tissue of the medulla i
. Modern surgery, general and operative. matory exudate enters into the blood-clot and theleukocytes eat up and destroy the clot. The clot is simply dead materialand in no way contributes to repair. The cells of the damaged tissue pro-liferate and the young proliferating cells (fibroblasts) enter into the spaces inthe clot which were eaten out by the leukocytes. Finally, the entire clot isreplaced by fibroblasts and much of this cellular mass quickly becomes vas-cularized (granulation tissue). The osteoblasts which exist in the deeper layers of the periosteum and,in the tissue of the medulla itself, begin to proliferate actively soon after thefracture has taken place. The fibroblasts have been formed by the prolifera-tion of the ordinary connective-tissue cells, and the proliferating osteoblastssoon enter into and become widely distributed through this mass of observers maintain that the fibroblasts themselves are directly trans-formed into bone; others deny this, and think that all bone formation comes from. Fig. 307.—Compound fracture. the osteoblasts. Osteoblasts may form bone directly, or may form cartilagefirst and then bone. When a fracture takes place, a bridge of periosteum isusually left untorn, and this bridge holds the fragments in contact at some point,just as a strap nailed to a trunk and also to its lid holds these two objectsin contact at some point. The new tissue about the periosteal bridge alwaysbecomes cartilaginous for a time, but the rest of the callus rarely shows the de-velopment of cartilage, and passes directly into bone. If, however, osteoblastsfail to proliferate with sufficient activity, the mass of granulation tissue becomesfibrous tissue; bone is not formed at all, or is very scantily formed, and fibrousunion occurs. If the osteoblasts lack activity, but are more active than in thecase just cited, they form cartilage extensively—but cartilage only; conse-quently, cartilaginous union occurs. During the process of the
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