I I 2 THE TISSUES. 



cartilage in men about the fortieth year, and in women about the 

 sixtieth year. 



To obtain chondrin, a piece of cartilage matrix is placed in a 

 tube containing water. This is hermetically closed and heated to 

 120 C, after which it is opened and the fluid filtered and treated 

 with alcohol. A precipitate of chondrin is the result. This sub- 

 stance is insoluble in cold water, alcohol, and ether, but soluble in 

 hot water, although, on cooling, it gelatinizes. In contrast to gel- 

 atin, chondrin is precipitated by acetic acid. This precipitate does 

 not redissolve in an excess of this acid but disappears in an excess 

 of certain mineral acids. 



6. BONE. 



(a) Structure of Bone. Bone nearly always develops from a 

 connective-tissue foundation, even where it occurs in places formerly 

 occupied by cartilage. 



The inorganic substance of bone is deposited in or between the 

 fibers of connective tissue, while the cells of the latter are trans- 

 formed into bone-cells. 



As in connective tissue, so also in bone, the ground-substance 

 is fibrous. Between the fibers remain uncalcified cells, bone-cells. 

 each of which rests in a cavity of the matrix lacuna. 



Primarily, bone consists of a single thin lamella, its later com- 

 plicated structure being produced by the formation of new lamellae 

 in apposition to the first. During its development the bone becomes 

 vascularized, and the vessels are inclosed in especially formed canals 

 known as vascular or Haversian canals. 



The bone-cells have processes that probably anastomose, and 

 that lie in special canals known as bone canaliculi. Whether, in 

 man, all the processes of bone-cells anastomose is still an open 

 question. 



The appearance presented by a transverse section of the shaft 

 of a long bone is as follows : In the center is a large marrow cavity, 

 and at the periphery the bone is covered by a dense connective- 

 tissue membrane, the periosteum. In the new-born and in young in- 

 dividuals the periosteum is composed of three layers an outer layer, 

 consisting mainly of rather coarse, white fibrous-tissue bundles that 

 blend with the surrounding connective tissue ; a middle fibro-elastic 

 layer, in which the elastic tissue greatly predominates ; and an inner 

 layer, the osteogenetic layer, vascular and rich in cellular elements, 

 containing only a few smaller bundles of white fibrous tissue. In 

 the adult the osteogenetic layer has practically disappeared, leav- 

 ing only here and there a few of the cells of the layer, while 

 the fibro-elastic layer is correspondingly thicker (Schulz, 96). A 

 large number of Haversian canals containing blood-vessels, seen 

 mostly in transverse section, are found in compact bone-substance. 



