DIGESTION A^n FOOD. 29 



CHAPTER V. 



Motions of the Stomach. Digested Food homogeneous. Heat of 

 Stomach during Digestion. Cold interrupts Digestion. Py loric 

 Valve. 



46. THIS mixture of the fluid with the food in the stomach 

 is aided by the action of its muscular coat, and of the 

 muscles of respiration. The muscular coat habitually re- 

 duces the size of the sack down to its contents. When 

 more food or drink is received, it relaxes, and allows the sack 

 to expand and give the new matter room. But this coat is 

 uneasy. It not only relaxes, but it again contracts, and 

 presses upon the food ; and then again it loosens. This is 

 repeated gently and continually; and by this means the 

 food is kept in slight motion, as long as the process of diges- 

 tion is going on. These movements are assisted by the 

 muscles of respiration. The stomach lies in the upper part 

 of the abdomen, (Fig. V. /,) and just below the chest, where 

 the lungs are situated. 



47. Immediately above, and in contact with the stom- 

 ach, the diaphragm (Fig. V. d) stretches across the body 

 from side to side, and from the back-bone to the breast- 

 bone. This great muscle is the partition wall between the 

 chest and the abdomen, and moves with every breath. 

 Every time we draw our breath, this presses downwards 

 upon the stomach, enlarges the cavity of the chest, and gives 

 room for the air to flow into the Jungs. Then, when \ve 

 exhale, the abdominal muscles those which principally con- 

 stitute the front wall of the abdomen contract, press upon 

 the stomach, and throw it upon the diaphragm, and force the 

 air outward. Thus the stomach is kept in incessant motion. 

 Every inspiration of air presses it downward and outward, 

 and every expiration presses it upward and inward. These 

 combined movements keep the food in such agitation, that it 

 becomes thoroughly mixed with the gastric juice, and the 



3* 



