DIGESTION 125 



They are squeezed towards the pylorus, which opens at intervals 

 to let them through. If lumps of solid matter reach it, the 

 pyloric valve closes tightly, until the undigested food has 

 fallen back into the dependent bag. Dyspeptics are sometimes 

 unpleasantly conscious of the contractions of the pyloric funnel. 

 In fact, putting aside pain due to gastritis, all the discomfort 

 of dyspepsia is felt on the right side. Flatus accumulates 

 beneath the pyloric valve. The valve will not open to let it 

 pass. The pyloric portion of the stomach contracts strongly. 

 Notwithstanding the general trend of movement in the opposite 

 direction, the gases are squeezed back into the larger bag, and 

 escape through the cardiac orifice. 



Tables have been prepared showing the length of time 

 which various articles of food take to digest. They are based 

 in part upon observations made upon the living stomach in 

 cases in which it has been possible to examine its contents 

 through a fistulous opening ; in part upon the results of arti- 

 ficial digestions carried out in the laboratory. It is hardly 

 too much to say that such observations are absolutely without 

 value as tests of the relative digestibility of the several articles 

 of diet consumed as parts of an ordinary meal. The fact that 

 the commencement of the flow of gastric juice depends upon 

 mental stimuli, and its continuance upon hormones, shows how 

 difficult it must be to reproduce the conditions which obtain 

 in a healthy living body. The most wholesome of foods taken 

 by itself may be longer in digesting, or may produce more 

 irritation, than many less desirable things taken in judicious 

 combination. Crushed chicken, hastily swallowed, sometimes 

 proves more difficult of digestion than meat so cooked and 

 served as to stimulate appetite and to demand mastication. 



Returning to the story of a meal, vegetables pass almost 

 unaltered through the stomach. Some of the scanty proteins 

 which they contain are peptonized, but unless they are very 

 well masticated or cooked until they are soft, and therefore 

 easily pulped by the churning action of the stomach, the 

 gastric juice has to reach the proteins through-Ccell- walls. 

 None of the digestive juices are able to dissolve the cellulose 

 of vegetable cell- walls. Blocks of vegetable tissue pass down 

 the whole length of the alimentary canal in the form in which 

 they were left by the teeth. Hence the extreme indigestibility of 



