THE GROWTH OF BONE 63 



the brachial artery of a young patient in consequence 

 of the penetration of the vessel by a spicule of the 

 humerus, which was fractured. Osteoblasts washed 

 out of the humerus were thus distributed throughout 

 the clot lining the aneurysm, and it developed a 

 regular bony wall. This would probably occur more 

 frequently when the aorta erodes the vertebrae, but 

 for the fact that in that case the patient's osteoblasts 

 are usually senile. 



In some experiments, after removing a length of 

 the radius with its periosteum, the gap was filled 

 with bone chips. Consolidation took place, but a 

 large tumour-hke mass of callus formed, infiltrating 

 the surrounding muscles. The osteoblasts from each 

 chip had wandered out and proliferated, and when 

 they became mature had surrounded themselves 

 with calcareous deposit, which bound together not 

 only the detached fragments and the broken ends, 

 but also the muscles and tendoiis in the neighbour- 

 hood. 



The experimental and chnical work of Hey Groves 

 on fractures strongly supports the view that callus is 

 derived from bone and not from periosteum. 



The factors which induce bone-corpuscles to 

 become active and proliferate are not perfectly 

 understood. Macewen lays stress on relief from 

 pressure, and no doubt this has great importance. 

 Dissemination of osteoblasts by increased vascularity 

 of the part is another factor. The periosteum, when 

 intact, limits the osteoblasts to their own proper 

 sphere, and prevents their encroaching on the 

 muscles and fascial planes. 



