CARTILAGE. 69 



the middle of the cell a large clear vesicular nucleus with a dis- 

 tinct nuclear membrane, and one or more nucleoli. There are 

 seldom found two nuclei in one cell. Often the protoplasm 

 contains fat and glycogen droplets. The presence of the first is 

 easily demonstrated by perosmic acid, which turns the fat black. 

 The second may be shown by treatment with iodine solution, 

 which stains the glycogen brownish red. Pigment granules are 

 seldom found in cartilage. 



In the more superficial layers the cells are usually more flat- 

 tened, spindle-shaped, and smaller than the cells of the deeper 

 layers. They are on the outer surface arranged in parallel 

 rows. In some animals the cell body sends out processes, and 

 has a stellate appearance like a bone cell. This is seen mainly 



FIG. 3t>. 

 Empty cartilage cell cavity ^^ , Capsule 



Hyaline ground p 



substance" t~~~ 





^Vx ^EB Ifod*** f 



Empty en rt Uaoe^JU M^jj" cartilage cell 



cell cavity 



i .-_Jrl . u^cjgao.. jb J 



Hyaline cartilage. From a .section through the thyroid cartilage of the cat. X 190. 



in the lower animals (cephalopods, selachians), and only in a 

 few places in some mammals. It is noticed also in pathological 

 new formations (endochondromata). Cartilage cells vary from 

 3 to 30 u in diameter. They increase usually by indirect divi- 

 sion, but direct division has also been observed. 



The ground substance in the cartilage of higher animals is 

 very abundant. If we examine a thin section of fresh hyaline 

 cartilage, we notice that the ground substance appears quite 

 homogeneous and structureless, and contains the so-called carti- 

 lage spaces. Some time after death, however, and in cartilage 

 treated with reagents (e. g., water), the cells shrink and between 

 them and the boundaries of the spaces there appears an empty 

 area which allows the outlines of the cells to be plainly made 



