THE BODY ORGANIZATION 



3 



protoplasm forms all parts of the cell, this substance is 

 more properly called the cytoplasm, or cell plasm. Sur- 

 rounding and inclosing the cytoplasm, in many cells, is a 

 thin outer layer, or membrane, which affords more or less 

 protection to the contents of the cell. This is usually 

 referred to as the 

 cell-wall. A fourth 

 part of the cell is 

 also described, being 

 called the attraction 

 sphere. This is a 

 small body lying 



near the nucleus 



j . t^M-CsJKl^i.^xXrj;^-*-- 



and cooperating \^|iw^(9S 



with that body in 5 -K^raKr^ifcS^Xli 



the formation of 

 new cells. Food par- 

 ticles, wastes, and 

 other substances w , FlG \ 4 " ~ ^/P" 11 , of a ty P ic f cel1 (after 



Wilson). I. Mam body. 2. Nucleus. 3. At- 



may also be present traction sphere. 4. Food particles and waste, 

 in the Cytoplasm. 5- Cell-wall. 6. Masses of active material found 

 T-,I r . in certain cells, called plastids. 



1 he parts of a typi- 

 cal cell are shown in Fig. 4. 



Importance of the Cells. The cells must be regarded 

 as the living, working parts of the body. They are the 

 active agents in all of the tissues, enabling them to serve 

 their various purposes. Working through the tissues, they 

 build up the body and carry on its different activities. 

 They are recognized on this account as the units of struc- 

 ture and of function, and are the "individuals" in the 

 body organization. Among the most important and inter- 

 esting of the activities of the cells are those by which they 

 build up the body, or cause it to grow. 



