LIVING BODIES AND CELLS 



II 



through the body. Each collection does its own work, 

 without interfering with the others. The cells work 

 together like a well-trained army, so 

 that we do not feel the workings of 

 each separate cell. If a collection is 

 out of order, the person is sick. 



4. Cells. Cells are of various 

 shapes, according to the work they 



have to do. They are from ^ to Plants and animalsound 

 T ^0 of an inch in length. Each cell in stagnant water, each con- 

 . .., i i n 1-1 i sistingofasinglecell(X20o). 



is like thick jelly and is almost color- 

 less. Near its center a small mass of slightly different 

 composition may usually be distinguished. This central 



mass is called the nucleus. 

 The substance composing 

 the cell is like the white of 

 an egg and is called proto- 

 plasm. Although proto- 

 plasm is 

 transpar- 

 ent and 

 jellylike, 

 yet under 

 a micro- 

 scope 

 there ap- 

 pears an interlacing series of beads and 

 lines which suggest a structure as com- 

 plex as that of the body itself. 



5. Connective tissue. The cells are 



kept in place by a fine network of strong fibers called con- 

 nective tissiie. In some parts of the body, as on the outside 

 of the muscles, it is thick and skinlike, but around each 



Cells from the human body (X 200). 



a A colored cell from the eye. 



b A white blood cell. 



c A connective tissue cell. 



d A cell from the lining of the mouth. 



e Liver cells. 



/ A muscle cell from the intestine. 



Diagram of the parts 

 of a cell. 



a Nucleus. 



b Cell-body or proto- 

 plasm. 



c Covering, generally 

 absent in animal 

 cells. 



