58 THE CONNECTIVE TISSUES. [CH. V. 



origin of the whole matrix, but intercellular material accumulates 

 outside the capsules and still further separates the cells. 



By certain complicated methods of double staining this twofold 

 manner of formation may be shown very markedly. We have 

 seen that chondrin obtained by boiling cartilage is really a 

 mixture of two substances ; one is a mucinoid material, and 

 comes from the capsules ; the other is gelatin, which comes from 

 the rest of the ground-substance which is collagenous. In hyaline 

 cartilage, however, the collagen does not become precipitated to 

 form fibres, but in white fibro-cartilage it does. In yellow fibro- 

 cartilage the matrix is pervaded by a deposit of elastin, which 

 results in the formation of a network of clastic fibres. 



Bone. 



Chemical composition. Bone is composed of earthy and animal 

 matter in the proportion of about 67 per cent, of the former to 

 33 per cent, of the latter. The earthy matter is composed chiefly 

 of calcium phosphate, but besides this, there is a small quantity 

 (about 1 1 of the 67 per cent.) of calcium carbonate, calcium 

 fluoride, and magnesium phosphate. 



The animal matter is chiefly collagen, which is converted into 

 gelatin by boiling. 



The animal and earthy constituents of bone are so intimately 

 blended and incorporated the one with the other that it is only 

 by severe measures, as for instance by a white heat in one case 

 and by the action of concentrated acids in another, that they can 

 be separated. Their close union too is further shown by the fact 

 that when by acids the earthy matter is dissolved out, or on the 

 other hand when the animal part is burnt out, the shape of the 

 bone is alike preserved. 



The proportion between these two constituents of bone varies 

 slightly in different bones in the same individual and in the 

 same bone at different ages. 



Structure. To the naked eye there appear two kinds of struc- 

 ture in different bones, and in different parts of the same bone, 

 namely, the dense or compact, and the spongy or cancellous tissue. 

 Thus, in making a longitudinal section of a long bone, as the 

 humerus or femur, the articular extremities are found capped on 

 their surface by a thin shell of compact bone, while their interior 

 is made up of the spongy or cancellous tissue. The shaft, on the 

 other hand, is formed almost entirely of a thick layer of the com- 

 pact bone, and this surrounds a central canal, the medullary 

 cavity so called from its containing the medulla or marrow. 



