SUMMARY OF PART I 215 



SUMMARY OF PART I 



The body is an organization of different kinds of cells ; 

 it grows through the growth and reproduction of these 

 cells ; and its life as a whole is maintained by providing 

 such conditions as will enable the cells to keep alive. Of 

 chief importance in the work of the body is a nutrient fluid 

 which supplies the cells with food and oxygen and relieves 

 them of waste. A moving portion of this fluid, called 

 the blood, serves as a transporting agent, while another 

 portion, called the lymph, passes the materials between 

 the blood and the cells. Through their effects upon the 

 blood and the lymph, the organs of circulation, respiration, 

 digestion, and excretion minister in different ways to the 

 cells, and aid in the maintenance of life. By their com- 

 bined action two distinct movements are kept up in the 

 body, as follows : 



1. An inward movement which carries materials from 

 the outside of the body toward the cells. 



2. An outward movement which carries materials from 

 the cells to the outside of the body. 



Passing inward are the oxygen and food materials in a 

 condition to unite with each other and thereby change their 

 potential into kinetic energy. Passing outward are the 

 oxygen and the elements that formed the food materials 

 after having united at the cells and liberated their energy. 



As a final and all-important result, there is kept up a 

 continuous series of chemical changes in the cells. These 

 liberate the energy, provide special substances needed by 

 the cells, and preserve the life of the body (Fig. 92). 



In the chapters which follow, we are to consider the 

 problem of adjusting the body to and of bringing it into 

 proper relations with its surroundings. 



