294 DIGESTION. 



Movements of the Stomach. 



It has been already said, that the gastric fluid is assisted 

 in accomplishing its share in digestion by the movements 

 of the stomach. In granivorous birds, for example, the 

 contraction of the strong muscular gizzard affords a neces- 

 sary aid to digestion, by grinding and triturating the 

 hard seeds which constitute part of the food. But in the 

 stomachs of man and Mammalia the motions of the mus- 

 cular coat are too feeble to exercise any such mechanical 

 force on the food ; neither are they needed, for mastication 

 has already done the mechanical work of a gizzard ; and 

 the experiments of Reaumur and Spallanzani have demon- 

 strated that substances enclosed in perforated tubes, and 

 consequently protected from mechanical influence, are yet 

 digested. 



The normal actions of the muscular fibres of the human 

 stomach appear to have a three-fold purpose; first, to 

 adapt the stomach to the quantity of food in it, so that its 

 walls may be in contact with the food on all sides, and, at 

 the same time, may exercise a certain amount of com- 

 pression upon it; secondly, to keep the orifices of the 

 stomach closed until the food is digested ; and, thirdly, to 

 perform certain peristaltic movements, whereby the food, 

 as it becomes chymified, is gradually propelled towards, 

 and ultimately through, the pylorus. In accomplishing 

 this latter end, the movements without doubt materially 

 contribute towards effecting a thorough intermingling of 

 the food and the gastric fluid. 



When digestion is not going on, the stomach is uniformly 

 contracted, its orifices not more firmly than the rest of its 

 walls ; but, if examined shortly after the introduction of 

 food, it is found closely encircling its contents, and its ori- 

 fices are firmly closed like sphincters. The cardiac orifice, 

 every time food is swallowed, opens to admit its passage 

 to the stomach, and immediately again closes. The pyloric 

 orifice, during the first part of gastric digestion, is usually 



