THE CELL 



31 



general pattern of cell organization is very much alike in all cells. 

 Studied in one cell, this pattern serves as an interpretation of the 

 arrangement of cell substances in any other cell. The study of cells 

 and intracellular structures is called cytology. 



Shape of Cells. It is not possible to state that cells assume 

 any particular shape. If the cell contents were a pure liquid and 

 the cell were not confined, its shape would be spherical, due to 

 the fact that the surface tension of drops of pure liquids impels 

 the drops to a spherical shape— the law of minimal surfaces. But in 



^ B C D £ 



Fig. 5. — Diagrams illustrating several t>^pes of cell shapes. A, columnar, as arc 

 the cells forming the lining of the human intestine; B, pavement, the shape and 

 arrangement of cells lining the bladder; C, spindle, as the muscle cells in the wall 

 of the stomach; D, nerve, the general shape of nerve cells in the spinal cord; E, 

 cylindrical, characteristic of the long muscle cells which make up the large voluntary 

 muscles. In addition to those illustrated, plant and animal cells assume many 

 other shapes. 



many cells the protoplasm Is a stiff jelly which resists a tendency 

 to form a sphere. In other cells the contents are confined and the 

 cell has the shape imposed by the confining walls. The shape of 

 some cells is determined by the fact that they are compressed to- 

 gether. But in general, the shape of the cell is as peculiar to it as 

 are its other features and functions, an expression of its organi- 

 zation (Fig. 5). 



Function of Cell Structures. The fact that these different 

 intracellular types of protoplasm differ in appearance, react dif- 

 ferently to chemical agents and to artificial staining, and are regu- 

 lar in location and behavior in all cells, proves that protoplasm in 



