316 THE TISSUES. 



What are the precise chemical characters of the cartilage-cells 

 and their contents, is unknown. 



The amount of water varies in the different true cartilages be- 

 tween 54 and 70 per cent. (Lehmanri)\ and exerts an important 

 influence on their physical properties. 



The fat constitutes from 2 to 5 per cent, of the dry cartilage. 

 Mulder first proved that a small amount of sulphur is combined 

 with the chondrine (cartilageine). It, therefore, probably exists in 

 the intercellular substance alone. In the costal cartilages from 3 to 6 

 per cent, of mineral substances have been found, viz., phosphates of 

 lime and magnesia, chloride of sodium, carbonate of soda, and a 

 large amount of sulphates. The chloride of sodium varies ex- 

 tremely in the ash of cartilage (from 1 to 8 per cent.) ; there, how- 

 ever, being more of it in cartilage than in any other tissue. (Leh- 

 mann.) These variations suggest the idea that it is combined not 

 with the histological elements of the cartilage, but exists in the 

 peculiar fluid which permeates the intercellular substance. 



Properties and Uses of Cartilage. 



True cartilage manifests only physical, and no vital properties, 

 in the organs of which it forms a part ; viz., solidity and elasticity. 

 When fully developed, cartilages contain no vessels at all; and 

 hence constitute an extra- vascular tissue, like the cornea and epi- 

 thelium and its modifications (p. 281). Nor do they contain lym- 

 phatics or nerves. 1 



Uses. The uses of the true cartilages depend on the two proper- 

 ties just noticed. Hence they are found where a tissue is required 

 to resist pressure, as in the articular cartilages ; whose elasticity and 

 insensibility (from possessing no nerves) are at the same time put 

 into requisition. The costal cartilages afford sufficient strength for 

 the walls of the thorax, while their flexibility and elasticity favor 

 the movements of respiration. The cartilages of the nose afford 

 to that organ the requisite firmness and flexibility. 



Finally, cartilages exist in the embryo instead of bones ; and 

 which finally assume the form of the bones to be subsequently de- 

 veloped. These subsequently giving place to the bones, and thus 

 disappearing, are termed temporary cartilages, and in their aggre- 

 gate, constitute the cartilaginous skeleton ; while the others in the 



1 In the septum narium of the calf, Kolliker found both arteries, and small nerv- 

 ous twigs. The costal cartilages also contain a few vessels. 



