100 STUDIES IN CLINICAL PHYSIOLOGY 



spasmodic contraction of the sphincter which is 

 relaxed only during swallowing, vomiting , or eructa- 

 tion of gas or fluid. 



Shape, Position, and Movements of the 

 Stomach. — The stomach consists of two distinct parts, 

 which behave quite differently during digestion. The 

 cardiac end and the greater part of the body form 

 an oval reservoir lying vertically, with a well-marked 

 angular ring separating it off from the horizontal or 

 ascending narrow tubular pyloric antrum. After 

 death, or under an anaesthetic, this distinction is lost, 

 but it is often seen in formalin-hardened bodies. 

 Just after a meal, the greater curvature forms the 

 lowest point, and in men while standing it falls a 

 few centimetres below the umbilicus. Later, as the 

 stomach shortens, the pylorus becomes the lowest 

 point. 



After an ordinary meal, movements of peristalsis 

 start, usually about the middle of the cardiac reser- 

 voir, and advance in regular waves towards the 

 pylorus, which remains tightly closed. In man, the 

 waves are about three to the minute, and keep on so 

 long as there is food present. The consequence is 

 that the gastric contents become thoroughly mixed 

 with the digestive juices. After a while, when 

 these contents are sufficiently acid, the pylorus 

 begins to yield momentarily at intervals, and to let 

 the food through into the duodenum. Whilst acid 

 is present on the far side, the sphincter remains 

 closed ; when it is neutralized it opens again. Tlius 

 acid in the stomach opens the pylorus ; acid in 

 the duodenum closes it. This goes on until the 



