Studies from the laboratories of the Deptof Surgery . ume that the osteoblast is a specific cell coming from otherbone cells. Moreover, it is impossible to explain the formation of bonein the arteries of human beings, in the lymph nodes or in the kidneyby either of these theories. If we assume that bone is formed by metaplasia of connective tissuecells into osteogenetic cells or if we assume that it is purely a chemicaldeposition in living connective tissue, we may explain the phenomenonvery easily. 16 The third theory has seemed more plausible to nie. Gideon Wellshas shown that if cartilage i
Studies from the laboratories of the Deptof Surgery . ume that the osteoblast is a specific cell coming from otherbone cells. Moreover, it is impossible to explain the formation of bonein the arteries of human beings, in the lymph nodes or in the kidneyby either of these theories. If we assume that bone is formed by metaplasia of connective tissuecells into osteogenetic cells or if we assume that it is purely a chemicaldeposition in living connective tissue, we may explain the phenomenonvery easily. 16 The third theory has seemed more plausible to nie. Gideon Wellshas shown that if cartilage is transplanted into the omentum it has agreater power of absorbing calcium from the blood than has any othertissue similarly placed. He believes that the same proportions ofcalcium phosphate and calcium carbonate are present in the ash ofcalcified material as bone, the main difference being that calcificationoccurs in dead tissue while ossification occurs in the presence of livingtissue. In sections of kidneys in which the vessels have been ligated,. Fig. 15.—Cross-section showiiij^ massive sequestrum, with thick involucrumand zone of separation: SQ, sequestrum; lu, involucrum; S, zone of separation. there are zones of calcification and ossification, the calcification occurringin dead tissue and ossification occurring where living bone cells areobserved. The simplest ty[>e of bone repair is seen following fractures. In aseries of fractures on animals, I have been able to follow the repairat various stages. Immediately following the fractures, there is hemor-rhage between the broken ends. Fibrin is then deposited and con- 17 traction of the clot occurs. In from about tive to ten days theorganization of the clot by the ingrowth of connective tissue tissue appears to take a definite lobulated arrangement, sothat if we look at a cut section, we find blood vessels and then areasof thin areolar connective tissue (Figs. 1 to 4). Calcium salts are then deposited
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