THE LI \ ING MATERIAL OF THE BODY 



15 



FIG. 6. CONNECTIVE TISSUE 



A bit of tendon highly magnified. 

 At C are shown some of the cells 

 which produced the fibres. 



cells, is given the main credit of firmly establishing what has 

 since been known as the cell theory of tissue structure. 



According to some students of the subject, these cells are 

 connected, each with its neighboring cells, by very tiny, hollow 

 tubes ("bridges"); but others are equally certain that each cell 



acts by itself, save as fluids may 

 pass out from each cell and be 

 carried to other cells of the body 

 in trie blood stream. 



Kinds of Cells. The shape of 

 these cells is different in differ- 

 ent kinds of tissues, just as bricks 

 used in the foundations of build- 

 ings differ from those employed 

 for fireplaces or ornamental work. 

 Epithelial cells are thin and disc-like or cylindrical in shape 

 (Fig. 3 a, b, c and d) and usually have very little space be- 

 tween them. 



Cartilage cells are round or hemi- 

 spherical and are usually more widely 

 separated; Fig. 4. The material be- 

 tween them, intercellular substance, has 

 been formed by the cells themselves 

 and secreted in large quantities, sep- 

 arating them as mortar does bricks. 



Bone cells are close together in very 

 young bone, but later are separated by 

 a secretion which they deposit around 

 themselves. This deposit contains a 

 mineral matter, calcium phosphate, which 

 causes the mass to harden. As the bone 

 develops, this hard mineral matter be- 

 tween the cells becomes very abundant, and finally, in the fully 

 formed bone, the cells proper occupy very small spaces; Fig. 5. 

 Connective tissue shows almost no cells for it consists for 

 the most part of numerous fine fibres, frequently arranged 



FIG. 7. CONNECTIVE 



TISSUE 



The soft tissue that lies 

 between the skin and the 

 muscles. Fibres are 

 shown running irregu- 

 larly, and some cells, C. 



