DEVELOPMENT OF CARTILAGE. 83 



Cartilage grows in two ways : (a) by the expansion produced by the inier- 

 stitial gro'wth effected by the formation of new cells and the associated matrix, and 

 (^) by the addition of the new 



tissue developed by perichon- Fig. 112. 



drial growth at the periphery of . .vV^..^T^^^M^ . ' ,,_ . .. vv> 



the cartilage from the chondro- \v ' ' f- ,^ ' -^ ^',. 



genetic layer. The latter mode ,^1^' .^'\ 



continues throughout the period ■■.,^T^«, "^^ '--s -' ^^^\ 



of growth, and mcludes the di- -^ ^ ^ 



reCt conversion of the COnneC- ' ^ '"^ —-r—Hyaline area 



,, f 1 . , < , I ^ I "-V --^ surrounding 



tive-tissue cells of the perichon- ^ - ^ ^ ^^ caniiage-ceiis 

 drium intothecartilage elements, v^ ^^ 

 and the accompanying formation \\^^ ^ '\ ^ -^ ' \^^^ 

 of new matrix. ' '«I<l ^jA \ ^ V-^ 

 The development of the - '^== ^| '^\!r4' 

 elastic fibres within the elastic ' ^ ^^ ^C'*^\ '^' 

 cartilage is secondary, the matrix X^, -^ r '^u' "- '^ 

 during the early stages of growth ' ' ' ^ - — — t — — ^ Fibrous inter- 

 being hyaline. The elastic tis- ^ .^ -%; sS"ce'''"'" 

 sue first appears in the form of "~vv^\ '"^j,-''' - ''^' 

 minute granules, which later ^ ^^aJ^' ' '* "Vn =^ ^J-^^^^, 

 fuse and become the elastic ' ^if^ , <^, ""^v' ^ 

 fibres ; this change first appears """' '5^ «-it ~~ ~ — Caniiage-ceiis 

 in the vicinity of the cartilage- -? 

 cells, the elastic reticulum sub- Sfev^j.vUi\\^4%-:<i^ Oi' 

 sequently invading the more re- ^^^ '^ ^.n,.^ .^, .^<;;..^'=^i 



mote portions of the matrix. In section of fibrous cartilage from intersertebral disk. X 225. 



the development of the fibro- ^ 



cartilage, the fibres appear coincidently with the limited pericellular areas of hyaline 



substance. 



Chemical Composition of the Connective Substances. 



Connective Tissue. — The fibrils of white fibrous connective tissue consist of a 

 substance known as collagen. The interfibrillar ground-substance contains mainly 

 mucoid and the albuminous materials, seruni globulin and serum albumin. Gelatiyi 

 is the hydrate of collagen, and is- obtained by boiling fibrous tissue with water, when 

 the gelatin separates like a jelly on cooling. In the case of the yellow elastic 

 fibres, elastin is found in place of collagen. In reticular tissue rcticulin is 

 found. The latter substance contains phosphorus. These substances, namely, 

 collagen with its hydrate gelatin, elastin and perhaps reticulin, are among those 

 known as albuminoids, which are closely related to the true albumins, yet differ in 

 some important respects. The albuminoids, for the most part, contain less carbon 

 and more oxygen than the albumins proper. 



Cartilage. — The fibres which are found in the matrix of fibro-cartilage and 

 elastic cartilage are respecti'^^ely composed of collagen and of elastin, just as they are 

 in the corresponding connective tissues. 



According to His, the chemical composition of human cartilage is as follows : 



Costal cartilage. Articular cartilage. 



Water 67.67 73.59 



Solids 32.33 26.41 



Organic matter 30.13 24.87 



Mineral salts , . 2.20 1.54 



In the mineral salts there is about 45 per cent, of sodium sulphate. A somewhat 

 smaller percentage of potassium sulphate, and smaller amounts of the phosphates of 

 sodium, calcium and magnesium, as well as of sodium chloride, are present. 



Adipose Tissue. — The fats in the animal body are mainly the triglycerides of 

 stearic, palmitic and oleic acid. There is found in man a comparatively large amount 

 of olein. Small quantities of lecithin, cholesterin and free latty acids are also found 

 in fat tissue. 



