100 MANUAL OF HISTOLOGY. 



the spaces disappear, and in place of them there is a single 

 dilated central cavity. 



Howship's lacunce are the pits or lacunae seen in bone 

 beneath the periosteum. They usually contain a multinuclear 

 corpuscle (giant-cell), which is in some way related to absorp- 

 tion, and, therefore, has received the name osteoclast (Kolli- 

 ker). It has been surmised (Klein) that they are the agents by 

 which an acid is formed that dissolves the lime-salts. Whether 

 they are developed out of the osteoblasts or not is a matter of 

 uncertainty. 



All the steps, both in development and absorption of bone, 

 have been carefully studied and placed upon a most satisfac- 

 tory foundation (Lieberkiihn and Bermann). The absorption 

 of bone has also been actually proved by measurements of the 

 bones in children (Schwalbe). By comparing the bones of the 

 third and fourth years of life, it was found that the marrow 

 cavity had enlarged in the latter, while the compact bone had 

 diminished in thickness. The change commenced at the sixth 

 month. This physiological process is closely allied to the 

 pathological one exhibited in rachitis ; in the latter the de- 

 velopment of bone from the periosteum has the character of 

 foetal bone, but the formation of the lamellae is slow and 

 incomplete. 



It has been claimed that the growth of bone takes place 

 by an expansion of the intercellular substance (Strelzoff), but 

 this is denied (Kolliker, Wegener, Schwalbe, and others). 

 The ossein appe'ars to increase somewhat, but it is at the ex- 

 pense of the bone- corpuscles, which are thereby diminished in 

 size. 



Formation of callus. The method is the same as in the de- 

 velopment from periosteum. A corpuscular blastema is devel- 

 oped from the periosteum and intermuscular tissue. This 

 presses in between the fibres and bundles of the loose con- 

 nective tissue, pressing them asunder, assuming considerable 

 volume. This new tissue is hyaline cartilage. In from three 

 to six weeks it ossifies, being in part directly transformed into 

 bone, in part mediately, i.e., through the agency of medullary 

 spaces and osteoblasts. Where the extremities of the bone are 

 widely separated there is a formation of bone in the medullary 

 spaces of the broken ends of the bones. The pre-existing bone- 

 corpuscles have no part in the new-formation. This compact 



