CELLS AND THE CELL THEORY 



27 



function. The stomach has its muscles and its secreting glands; 

 the foot has its muscles, bones, tendons, ligaments, nerves, etc. 

 The different kinds of substance which form the organs are 

 known as tissues, and usually each tissue contains only one kind 

 of material and has but one kind of duty to perform. For 

 example: muscles, bones, glands, nerves, 

 and tendons, each represent a distinct 

 tissue; each has its special function in 

 the organ, and each is different from the 

 other. Muscles have the power of con- 

 traction, bones are for support, etc. 



By studying these different tissues un- 

 der the microscope we shall find that 

 they, too, are made up of minute parts, 

 called cells, and that in most instances 

 each cell is essentially like all the other 



cells of the same tissue. This may be shown by examining 

 Figures 4 to 6, in which several kinds of tissue appear, each made 



FIG. 4. CELLS FORM- 

 ING CARTILAGE TISSUE 



FIG. 5. CELLS FORMING BONY TISSUE 



up of a large number of independent, similar cells. These cells 

 represent the ultimate units to which the analysis of the struc- 



