CARTILAGE. 51 



ducing characteristic groups and rows of cells such as^are shown in the 

 diagram. It has been reasserted that some of the cells undergo a mucoid 

 degeneration and become lost in the matrix. Around the entire cartilage 

 of the adults there is a connective tissue envelope, the perichondrium, 

 containing undifferentiated cells which by growth and division become 

 cartilage cells. They are added to its surface. The young generations of 

 cartilage cells are therefore at the periphery, and the old are in the center 

 of the cartilage. Between them an interesting series of cytomorphic 

 changes may be seen. The perichondrium contains vessels and nerves. 

 Blood vessels may extend into the cartilage of young embryos, and into 

 cartilages which are being replaced by bone, but ordinarily cartilage is 

 non-vascular, receiving its nutriment by diffusion through the matrix. 

 In surgical operations the preservation of the perichondrium may be of 

 importance, since it can produce new cartilage. 



Fig. 54, B, presents Prof. Mall's idea of the formation of precartilage 

 in mammals, differing from that just described which followed Dr. Stud- 

 nicka's work on fishes. In B, by the development of fibrils which are 

 exoplasmic structures staining with eosin, the nuclei and endoplasm 

 become "extruded from the syncytium" and lie in the intercellular spaces. 

 The exoplasm becomes transformed into the matrix of the cartilage. 

 The crowded condition of the nuclei in precartilage makes it difficult of 

 interpretation. 



Glycogen, which occurs in cartilage cells, is a carbohydrate resembling 

 starch and known as "animal starch." It is soluble in water, and soon 

 after death is converted into glucose. For these reasons it disappears 

 from ordinary sections. Fresh tissues preserved in strong alcohol, and 

 stained with tincture of iodine, exhibit glycogen as brownish red masses, 

 tending to be round, but often not sharply outlined. Glycogen is abundant 

 in embryos in the epithelium of the skin, in liver cells and striated muscles 

 and in cartilage cells. It is found in similar situations in the adult, espe- 

 cially in well-nourished individuals, but is apparently not as abundant 

 relatively as in the embryo. It occurs also in other cells. Its production, 

 like that of fat, may be considered a nutritive rather than a glandular 

 phenomenon. 



The matrix of cartilage chemically is a mixture of collagen, chondro- 

 mucoid, chondroitin sulphuric acid (in combination), and albuminoid sub- 

 stances (albumoid). [The old term "chondrin" really means little else 

 than the matrix of cartilage.] The collagen may occur in white fibers 

 which abound in the matrix of that form of cartilage called fibro-cartilage. 

 Elastic fibers predominate in the matrix of elastic cartilage, If, however, 

 on ordinary microscopic examination the matrix appears homogeneous, 



