48 FORMATION OF CALLUS. 



Fig. 9.* It is according to this from a peculiar sub- 

 stance, not ordinary cartilage, that bone is pro- 

 duced, and we now know that the effused fluid 

 of which the callus in fractures is formed, is in 

 some respects different from the cartilagi- 

 nous mould of bone, and that in fact bone 

 is developed in many parts of the body, as 

 in the human .skull for instance, without the. 

 existence of any previous cartilaginous basis. 



Formation of Callus. 



The most ancient opinion entertained in regard to the mode of 

 union between broken bones, was, that it was owing to the con- 

 cretion of a viscous fluid, or imaginary osseous juice poured out 

 between the fragments. This was the opinion of Haller. Du- 

 hamil demonstrated the fallacy of this belief, by numerous 

 experiments, and instituted a theory of his own which is much 

 nearer the truth. According to him the production of callus or 

 new bony matter, is owing to the swelling, elongation, and 

 subsequent adhesion between the periosteum and medullary 

 membrane of one fragment with the corresponding parts of the 

 other; and that from these membranes thus modified, bony 

 matter was deposited in the form of a ring on the exterior of 

 the bone and a plug in its medullary cavity, which held the 

 fragments together by passing across the cavity of fracture, and 

 sometimes by prolongations passing between them through the 

 cavity. John Hunter believed that the re-union of fractured 

 bones took place from the organization of the blood effused 

 around the fracture and between the fragments ; a doctrine 

 which now has few supporters. 

 The credit of giving the most faithful account of the forma- 



* Fig. 9. Bone corpuscles, a, magnified 450 diameters, which have here been 

 converted into bone cells, b. Branches of the bony cells which by their inoscu- 

 lations form a net work. They are called by Mttller the canaliculi calicophori. 

 It is not yet fully decided whether or not the cells and their branches are filled 

 with calcareous matter, or merely incrusted with it. The diameter of these 

 calcigerous canals (canalic. calicoph.) is reckoned at their largest parts to be 

 between one fourteen thousandth and the one twenty thousandth part of an inch. 



