MOVEMENTS OF THE STOMACH. 231 



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 necessary aid to di- 

 gestion, by grinding and triturating the hard seeds which con- 

 stitute part of the food. But in the stomachs of man and 

 Mammalia the motions of the muscular 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 demonstrated that substances inclosed 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 threefold 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 compression 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 py- 

 lorus. In accomplishing this latter end, the movements with- 

 out 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 orifices are 

 firmly closed like sphincters. The cardiac orifice, every time 

 food is swallowed, opens to admit its passage to the stom- 

 ach, and immediately again closes. The pyloric orifice, 

 during the first part of gastric digestion, is usually so com- 

 pletely closed, that even when the stomach is separated from 

 the intestines, none of its contents escape. But towards the 

 termination of the digestive process, the pylorus seems to offer 

 less resistance to the passage of substances from the stomach ; 

 first it yields to allow the successively digested portions to go 

 through it ; and then it allows the transit of even undigested 

 substances. 



From the observations of Dr. Beaumont on the man St. 

 Martin, it appears that food, so soon as it enters the stomach, 

 is subjected to a kind of peristaltic action of the muscular 

 coat, whereby the digested portions are gradually approxi- 



