DIGESTION OF FOOD: THE OESOPHAGUS 97 



chyme. In this mass after an ordinary meal, there should be 

 water, saliva, mucus, gastric juice, peptones, unchanged 

 proteid, dissolved sugars, unmodified starches, curdled milk, 

 fat droplets, shreds of connective tissue and vegetable cellulose, 

 the woody substance in plant structures. Responding to the 

 presence of this chyme, the muscles in the pyloric valve 

 relax and allow the food to pass on into the small intestine. 



The mere presence of chyme in the stomach does not pro- 

 voke the pyloric valve to open and let it pass through. This 

 would obviously be poor management should it happen 

 that the duodenum were already full, and completely busy 

 with its work on chyme previously received. It will be re- 

 membered that chyme is acid, as a result of hydrochloric 

 acid in the gastric juice. In contrast, the juices of the intestine 

 are alkaline; but it takes some time for the intestinal secre- 

 tions to overcome the acidity of material received from the 

 stomach. When this acidity is finally neutralized, however, 

 a message is sent from the intestine to the pylorus that all 

 is in readiness for a further installment of chyme from the 

 stomach, and the valve opens. Very unexpectedly this 

 message is sent, not through nerve fibres as most stimuli 

 are, but through the blood stream; this is a round-about 

 method, but it is the one used in this instance. 



