Regeneration of Bone. 247 



and ends by complete restitution of tlie most dense osseous sub- 

 stance. The special bone cells embedded in a dense solid calcified 

 matrix are unable to take part in the construction of new tissue 

 because they have no space for any activity. The osteoblasts of 

 the periosteum and marrow, the bone forming cells, are connective 

 tissue cells which possess the peculiar ability of giving origin to an 

 intercellular material with an affinity for lime salts or of them- 

 selves producing calcification of the matrix and thus supplying the 

 basic osseous material. They are, however, also capable of produc- 

 ing fibrillar connective tissue and may act precisely as fibroblasts; 

 and finally may become transformed into cartilage cells, form a 

 homogeneous inter-cellular material and remain in the lacunae 

 within the latter. In bone repair therefore there is first noted a 

 fibroplastic callus which becomes partly changed into cartilage and 

 later into calcified osseous tissue. Coincidently the blood vessels of 

 the bone proliferate, complete analogy to the vascularized fibro- 

 plastic callus existing in the healing of lesions of the soft parts. 

 The name callus is applied to the whole of the tissue arising in the 

 osteogenetic process, its origin giving the basis for differentiating 

 between periosteal and myelogenous callus; tliat portion which de- 

 velops between the separated fragments is known as the iiitcruicd- 

 iate callus. 



In the neighborhood of the seat of fracture all of the periosteal 

 and marrow cells and vascular endothelial cells become swollen, nu- 

 clear division actively proceeds, and cellular proliferation is so lux- 

 uriant that the capillaries are often found occluded by young endo- 

 thelial cells and giving off profuse vascular buds ; the whole cellular 

 callus forming a growth decidedly exceeding the diameter of the 

 bone itself (the widei tlie space between the bone fragments the 

 greater this mass). 



This callus, at first consisting of connective tissue and some- 

 times called the provisional callus, has to do with the removal of the 

 clotted blood occasioned by the fracture and other tissue remnants, 

 even of small splinters of bone (the limy material of which is dis- 

 solved by the proliferating cells), through phagocytic cells originat- 

 ing from its newly forming constituents. It has a bacon-like, cartilag- 

 inous appearance, surrounds the ends of the bone as a thick girdle, 

 occupies the medullary cavity at the level of the fracture and the 

 whole space between the broken ends. The newly formed material 

 is markedly in excess, and after calcification the osseous scar unites 

 the fragments as a clumsy, thick enlargement of the shaft of more 

 or less spindle shape, ^^'ith calcification, which renders the callus 



