276 A YEAR IN SCIENCE 



These fundamental processes are : 



1. Digestion 



2. Respiration 



3. Circulation 



4. Excretion 



5. Motion 



6. Sensitiveness 



7. Reproduction 



Digestion. Under this head we shall include all the 

 processes connected with the use of food. It must 

 first be taken into the body, after which it must be 

 changed into such a form that it can pass into the body 

 fluids. 



In all of the many celled animals, food when taken 

 into the body passes into a tube, which usually extends 

 throughout the length of the body and has two open- 

 ings. Occasionally, there is only one opening, the. mouth. 



The size and structure of this tube varies in different 

 animals. Usually it is divided into several regions, 

 such as the mouth, the throat, the esophagus, the stom- 

 ach, and the intestines. Frequently this latter part 

 is very much elongated so that the length of the digest- 

 ive tract, or alimentary canal, is very much greater 

 than the length of the body. 



Obviously, so long as the food is in this tube it can 

 not become a part of the body. Both the solid and 

 liquid foods must be acted upon physically and chem- 

 ically in such a way that they will diffuse through the 

 walls of the alimentary canal and into the vessels carry- 



