478 OF NUTRITION. 



latter, the fibrous network disappears by degrees towards the extremity of the 

 concha, and the structure gradually passes into the cellular form.* 



The substance that gives to the Cellular Cartilages their peculiar character, has re- 

 ceived the designation of Chondrin. It bears much resemblance to ordinary Gelatin, but 

 requires longer boiling in water for its solution; the solution fixes on cooling, like that 

 of gelatin, and when it becomes dry by evaporation it has the appearance of solid glue. 

 Chondrin is not precipitated, however, by tannic acid; on the other hand, it gives preci- 

 pitates with acetic acid, alum, acetate of lead, and protosulphate of iron which do not 

 disturb a solution of Gelatin. Its chemical constitution chiefly differs from that of 

 Gelatin in containing less nitrogen and more hydrogen ; its formula (as ascertained by 

 analysis before boiling) is 48 c,40 H,6 if, 20 o; and it may thus be regarded as composed 

 of 1 atom of protein, with 2 additional atoms of oxygen, arid 4 proportionals of waier. 

 Chondrin is not obtainable, however, from any of the Fibro-cartilages ; these yield gelatin, 

 on boiling, exactly similar to that of the tendons. The elastic cartilages, after being 

 boiled for several days, yield a small quantity of an extract, which does not form a jelly, 

 but which has the other chemical properties of Chondrin. The cartilage of Bone, before 

 ossification, yields only Chondrin ; after ossification, however, it affords only Gelatin; 

 and it is curious that even when bony deposits take place in the permanent cartilages, 

 the ossified portion contains ordinary Gelatin in the place of Chondrin. Many of the 

 cartilages naturally contain a large proportion of mineral matter; this is especially the 

 case with the costal cartilages, fractures in which are generally repaired by osseous 

 substance. The ash left by the calcination of these contains a large proportion of the 

 carbonate and sulphate of soda, together with carbonate of lime and a small proportion 

 of phosphate : as age advances, the phosphate of lime predominates, and the soluble 

 compounds diminish. The condition of the skeletons of the Cartilaginous Fishes ap- 

 pears to be nearly allied to this. 



626. Like the tissues already described, Cartilage (at least in its simplest 

 form) is nourished, without coming into direct relation with the Blood through 

 the medium of blood-vessels. From the inquiries of Mr. Toynbee it appears 

 that the cellular Cartilages are never penetrated by vessels in the healthy 

 state, although in certain diseased conditions they become distinctly vascular. 

 They are, however, surrounded by Blood-vessels ; which form large ampullae 

 or varicose dilatations at their edges or on their surfaces (Fig. 112) : and from 

 these the Cartilages derive their nourishment by imbibition ( 479), in exactly 

 the same manner as the frond of a Sea-weed (the structure of which is alike 

 cellular) draws into itself the requisite fluid from the surrounding medium. 

 When, however, the Cartilages are undergoing Ossification, large vessels are 

 seen in them ; and these vessels remain even when the Bone is fully formed. 

 This is well seen in the long bones, towards their extremities. At an early 

 period of foetal life, there is no distinction between the cartilage that is ultimate- 

 ly to become the Osseous Epiphysis, and that which is to remain as Articular 

 Cartilage; both are alike cellular; and the vessels that supply them with 

 nutrient materials penetrate no further than their surfaces. At a subsequent 

 period, however, when the ossification of the epiphysal cartilage is about to 



Fig. 112. 



Vessels situated between the articular cartilage and attached synovial membrane. (After Toynbee.) 

 * See Mr. Toynbee's Memoir on the Non- Vascular Tissues, Phil. Trans., 1841. 



