CARTILAGE 547 



and closely adheres to, the surface of the cartilage. It is 

 termed the perichondrium. The substance of the 

 cartilage itself is devoid of vessels ; it is hard, but not 

 very brittle, for it will bend under pressure ; and more- 

 over it is elastic, returning to its original shape when 

 the pressure is removed. It may be easilj' cut into very 

 thin slices, which are as transparant as glass, and to the 

 naked eye appear homogeneous. Dilute acids and akalies 

 have no effect upon it in the cold ; but if it is boiled in 

 water, it yields a substance similar to gelatin, but some- 

 what different from it, which is called chondrin. 



The sterno-costal cartilages of an adult man are many 

 times larger than those of an infant. It follows that 

 these cartilages must grow. The only source from whence 

 they can derive the necessary nutritive material is the 

 plasma exuded from the blood contained in the vessels of 

 the perichondrium. The vascular perichondrium therefore 

 stands in the same relation to the non-vascular cartila- 

 ginous tissue as the vascular dermis does to the non- 

 vascular epidermis. But, since the cartilage is invested 

 on all sides by the perichondrium, it is clear that no part 

 of the cartilage can be shed in the fashion that the 

 superficial layers of epidermis are got rid of. As the 

 nutritive materials, at the expense of which the cartilage 

 grows, are supplied from the perichondrium, it might 

 be concluded that the cartilage grows only at its surface. 

 But if a piece of cartilage is placed in a staining fluid, 

 it will be found that it soon becomes more or less 

 coloured throughout. In spite of its density, therefore, 

 cartilage is very permeable, and ' hence the nutritive 

 plasma also may permeate it, and enable every part to 

 grow. 



If a thin section of perfectly fresh and living cartilage 

 is placed on a glass slide, either without addition or with 

 only a little serum, it appears to the naked eye, as has 

 been said, to be as homogeneous as a piece of glass. But 

 the employment of an ordinary hand magnifier is sufficient 



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