196 THE MICROSCOPIST. 



consists essentially of stellate ramifying spaces containing 

 cells, and a hard, solid, intermediate substance. The latter 

 is composed of glutinous material rendered hard by a mix- 

 ture of inorganic salts, chiefly of calcium. 



As all bones are moulded first in cartilage it was natural 

 to conceive that they were developed by a transformation 

 of cartilage. Much variety of opinion still exists respect- 

 ing the process, but it is generally conceded that although 

 cartilage may undergo calcification, true bone is not formed 

 until the cartilage is dissolved, New generations of stel- 

 late cells appear in a matrix, which is first soft and then 

 calcified. New bone may also grow from the periosteum 

 by means of a stratum of cells called osteoblasts. The de- 

 tails of the process are too extensive for a treatise like the 

 present. If sections of growing bone are decalcified with 

 chromic acid and treated with carmine, the osteoblastic 

 layers and adjacent youngest bony layer acquire an in- 

 tensely red color, while the rest of the tissue, except the 

 bone-corpuscles, remains uncolored. 



Fine sections cut from a long bone longitudinally and 

 transversely will show the microscopic structure, consist- 

 ing of the' Haver sian canals (Plate XX, Fig. 151, a) sur- 

 rounded with concentric lamella? of compact structure (6, b). 

 There are also intermediate and periosteal lamellae (<?, d). 

 The cavities containing the bone-cells, or bioplasts (<?, <?,) 

 are of various sizes, from 0.0181 to 0.0514 millimetres 

 long, and from these lacunae run the canaliculi in an irregu- 

 lar radiating course (/,/). In a balsam-mounted specimen 

 these hollows sometimes retain air, by which the structure 

 is rendered more apparent. 



Dentine is the structure of which the teeth are most 

 largely composed. It consists of minute tubes filled with 

 bioplasm, which radiate from the central cavity of the 

 tooth, the interspaces between the tubes being solidified 

 by earthy salts so that the tissue is harder than bone. 



Histologically a tooth may be said to be made of three 



