CARTILAGE. 71 



an lime-water). In such preparations we see that it contains 

 fibrils, running usually in parallel lines and only excep- 

 tionally crossing one another. That they are not seen in the 

 living tissue is due to the fact that their refractive index is 

 nearly equal to that of the substance in which they live. The 

 reagents cause changes which make the difference between them 

 greater. Viewed with polarized light also, the fibrils may be 

 demonstrated. 



It is to be assumed that the metabolism in cartilage is not 

 active, because in higher animals there is only exceptionally 

 any vascular supply to the tissue, and no visible canal system 

 can be made out in which nourishing fluids could circulate. In 

 lower animals, however, canals can readily be recognized with- 

 out the use of reagents. These join the cartilage spaces with 

 one another, and form a system by which nourishing materials 

 may pass from one part of the tissue to another. Certain 

 authors (Spina, Budge, Wolters, etc.) have demonstrated canals 

 by means of special staining methods. These methods, how- 

 ever, involve the use of materials (e. g., water, alcohol, ether, 

 etc.) which cause shrinkage of cartilage, and it is possible that 

 the results obtained are artifacts. Similarly it is difficult 

 to say what parts take up the staining materials. It is possible 

 that the fibrils present in the ground substance act as paths for 

 the conduction of fluids from one part to another. In spite of 

 numerous recent investigations on the subject, the problems 

 concerning canals in cartilage are still unsolved. 



Cartilage possesses usually no blood-vessels. Only rarely, 

 and in places where active growth or ossification is going on, 

 are they present. The connective tissue and wandering cells 

 accompanying the vessels are known as the cartilage marrow. 



The perichondrium consists of white connective- tissue fibrils, 

 with only a very few elastic fibrils. These are arranged in 

 bundles which cross in different directions. The superficial 

 layers of cartilage usually pass over without sharp boundaries 

 into the perichondrium. This contains blood-vessels which, 

 under such conditions as are mentioned above, may grow into 

 the cartilage. During appositional growth the connective-tissue 



