250 HAND-BOOK OF PHYSIOLOGY. 



and ultimately through, the pylorus. In accomplishing this latter end, 

 the movements without doubt materially contribute toward 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 toward the termination of the digestive process, the pylorus 

 seems to oifer 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 por- 

 tions are gradually moved toward the pylorus. The movements were 

 observed to increase in rapidity as the process of chymification advanced, 

 and were continued until it was completed. 



The contraction of the fibres situated toward 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. 

 Martin, 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 toward the pyloric orifice for a dis- 

 tance of three or four inches. The object of this movement appears to 

 be, as just said, to carry the food toward the pylorus as fast as it is formed 

 into chyme, and to propel the chyme into the duodenum; the undigested 

 portions of food being kept back until they are also reduced into chyme, 

 or until all that is digestible has passed out. The action of these fibres 

 is often seen in the contracted state of the pyloric portion of the stomach 

 after death, when it alone is contracted and firm, while the cardiac por- 

 tion forms a dilated sac. Sometimes, by a predominant action of strong 

 circular fibres placed between the cardia and pylorus, the two portions, 

 or ends as they are called, of the stomach, are partially separated from 

 each other by a kind of hour-glass contraction. By means of the peri- 

 staltic action of the muscular coats of the stomach, not merely is chymified 

 food gradually propelled through the pylorus, but a kind of double cur- 

 rent is continually kept up among the contents of the stomach, the cir- 

 cumferential parts of the mass being gradually moved onward toward the 

 pylorus by the contraction of the muscular fibres, while the central por- 

 tions are propelled in the opposite direction, namely, toward the cardiac 

 orifice; in this way is kept up a constant circulation of the contents of 



