DIGESTION. 255 



Movements of the Stomach. The gastric fluid is assisted in accom- 

 plishing 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 digestion, by grinding and triturating 

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

 of man and other Mammalia the movements 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 experiments have demonstrated that substances are 

 digested even inclosed in perforated tubes, and consequently protected 

 from mechanical influence. 



The normal actions of the muscular fibres of the human stomach ap- 

 pear to have a three-fold purpose : (1) to adapt the stomach to the quan- 

 tity 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; (2) to keep the orifices of the stomach closed until the 

 food is digested ; and (3) to perform certain peristaltic movements, 

 whereby the food, as it becomes chymified, is gradually propelled to- 

 wards, and ultimately through, the pylorus. In accomplishing this lat- 

 ter 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 orifices 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 so completely 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 py- 

 lorus 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. 

 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 moved towards the pylorus. The movements 

 were observed to increase in rapidity as the process of chymification ad- 

 vanced, and were continued until it was completed. 



The contraction of the fibres situated towards the pyloric end of the 

 stomach seems to be more energetic and more decidedly peristaltic than 

 those of the cardiac portion. Thus, it was found in the case of St. Mar- 

 tin, that when the bulb of the thermometer was placed about three 

 inches from the pylorus, through the gastric fistula, it was tightly em- 

 braced from time to time, and drawn towards the pyloric orifice for a 



