40 THE CONNECTIVE TISSUES [CH. V. 



Thus the cells get more and more separated. The fused capsules 

 form a very large part of the matrix, and indications of their previous 

 existence may sometimes be seen in fully formed cartilage by the 

 presence of faint concentric lines around the cells. 



In a variety of cartilage found in the ears of rats and mice, called 

 cellular cartilage, the cells never multiply to any great extent, and 

 they are only separated by their thickened capsules. 



But in most cartilages the cell-capsules will not explain the 

 origin of the whole matrix, for intercellular material accumulates 

 outside the capsules and still further separates the cells. 



By certain 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 mucoid 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 per- 

 vaded by a deposit of elastin, which results in the formation of a 

 network of elastic fibres. 



Bone. 



Bone contains nearly 50 per cent, of water ; the solid material 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 11 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 the other, 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. 



To the naked eye there appear two kinds of structure 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 



