72 ELEMENTARY PHYSIOLOGY. 



The matter of the body all comes from 



fto^f JBtort!"* our foocL To P rovide our bodies with 

 such material, of good quality and of 



proper quantity, ought to be the main object of our 

 eating. Not all of the food matter which we eat is 

 useful in the body. So the means of separating the 

 useful from the useless is necessary. Then, again, 

 the useful part? of our food must be very much 

 changed before they can be used by the building 

 cells of the body. So the means for its proper prep- 

 aration must be furnished. The system whose or- 

 gans prepare the needed elements of tho food for 

 the blood, and separate the useless from the useful 

 portion, is called the digestive system. 



The preparation of food material for 

 *^ e blood requires many operations. 

 So the digestive system has a greater 

 number of special organs than any other system of 

 the body. We have seen how the movements and 

 work of the circulatory organs depend upon the 

 strength and prompt action of the muscles of the 

 heart; also, how the respiratory system depends upon 

 the muscular system in the steady and proper action 

 of the breathing muscles. So, here, as we study the 

 processes of the digestive system, we shall find how 

 its work depends upon the muscles which are assigned 

 to the duty of producing the necessary movements of 

 its organs. Even the muscles of the arm and hand 

 perform the very first act in the process of feeding 

 the body, in properly bringing the food to the mouth- 



