14 PHYSIOLOGY OF ALIMENTATION. 



food had not passed out of the stomach seven hours after 

 feeding. The same holds true for the human being, though 

 absolute quantity of food and its chemical and physical 

 character have much to do with its passage into the 

 duodenum. A large meal would, other things being equal, 

 take longer to leave the stomach than a smaller one. It 

 was pointed out above that coarse particles of food delay 

 the opening of the pylorus, and so keep a meal in the stomach 

 a correspondingly longer time. One of the pernicious results 

 of incomplete mastication of the food may well be traced 

 to this fact. We shall see below how the opening and closing 

 of the pyloric sphincter is affected still more powerfully by 

 the chemical constitution of the food. 



We can readily appreciate the value of an organ which, 

 as the stomach, retains the swallowed food and only little 

 by little passes it on into the intestinal canal beyond. In 

 this way the food does not become heaped up in any sec- 

 tion of the small or large bowel until the rectum is reached, 

 and greater chance for the chemical elaboration of the vari- 

 ous foodstuffs and for their absorption is obtained in con- 

 sequence. 



Having considered the movements of the stomach-wall, 

 we must discuss briefly the movements of the food within 

 the stomach. The older observations regarding this point 

 are very contradictory. 



As was shown above, waves pass rhythmically over the 

 antrum. The food squeezed forward by an undulation 

 may have one of two things happen to it. If the pylorus 

 is open the wave serves to push the food on into the duo- 

 denum. We saw above, however, that by no means every 

 wave is effective in this direction. For the majority of 

 waves it might almost besaid the pylorus remains closed. 

 Under these circumstances the food is forced into the blind, 

 pouch-like extremity of the antrum. When this occurs a 

 part at least of the food which is being pressed upon is forced 

 backward through the constriction towards the cardiac end 



