THE MOVEMENTS OF THE STOMACH 71 



easy to see how the cardia may be opened at the moment 

 when its muscular walls fall under the influence of the 

 phase of relaxation. Closure will follow immediately, as 

 the second or positive part of the peristalsis involves the 

 sphincter. Attention has been called to the fact that liq- 

 uids may outrun a pursuing peristalsis and arrive several 

 seconds in advance of it at the cardiac opening. Under 

 such circumstances it is said that the fluid remains at 

 the bottom of the esophagus until overtaken by the wave, 

 when the relaxation occurs which permits it to pass into 

 the stomach. A person drinking with ill-advised haste 

 may have the disagreeable experience of filling the esoph- 

 agus enough to produce a painful distention. Relief 

 comes abruptly when the peristalsis has made its way to 

 the cardiac sphincter and secured an entrance for the 

 liquid. 



While this has been the generally accepted description 

 of the facts, it has been shown recently that the cardia is 

 not always so firmly contracted. Observations by x-ray 

 methods, to be described presently, have shown that for 

 some time after a meal there may be a reflux from the 

 stomach of a cat into the esophagus. Each escape of food 

 evokes a local peristaltic wave which returns it to the 

 stomach. Such an incident does not entail any movement 

 of the throat muscles and is probably subconscious. As 

 the period of digestion continues the sphincter becomes 

 more tightly set and no longer allows any such return of 

 stomach-contents. The increased tension has a simple 

 explanation, which, like many another point about the 

 stomach, we owe toW. B. Cannon. He has shown that 

 the tension is developed in response to the rise of acidity 

 in the liquid just within the cardia. Since the acid appears 

 normally after each filling of the stomach, we have here 

 an automatic provision for the establishment of the requi- 

 site guard over this opening. The influence of the ner- 

 vous system seems capable of nullifying the local effect of 

 acid, since the sphincter may be relaxed to permit vomit- 

 ing at times when the gastric contents are excessively acid. 



