CELLS AND TISSUES OF THE BODY 



339 



blood vessels, and the esophagus, by which food is carried 

 from the mouth to the stomach. Below the diaphragm is 

 the abdomen, which contains the stomach, intestines 

 (bowels), liver, kid- 

 neys, pancreas, spleen, 

 etc. The thorax and 

 abdomen together 

 form the trunk. 



351. Cells and Tis- 

 sues of the Body. 



The human body, like 

 that of any plant or 

 animal, is composed 

 of cells. These cells 

 are living, and con- 

 sist of cell walls and 

 protoplasm (cf. 323). 

 Like the ameba (cf. 

 333) they carry on 

 the fundamental pro- 

 cesses of life. They 

 feed, and they reject 

 the waste from their food. They also reproduce them- 

 selves by the process of cell-division (cf. 323). Unlike 

 the cells formed by the division of an ameba, however, 

 the new cells of our bodies do not separate from the old 

 ones, but remain together. In this way the whole body 

 can grow, and new cells can at once replace those that die. 



Since the cells of our bodies form a large community, the division 

 of labor is necessary (cf, 346). Hence we find special groups of cells 



FIG. 273. 

 The Principal Organs of the Thorax and the Abdomen. 



