716 PHYSIOLOGY OF DIGESTION AND SECRETION. 



than a second elapses between the beginning of the contraction of 

 the mylohyoids and the entrance of the food into the upper end of 

 the esophagus. 



The passage of the food through the esophagus differs apparently 

 with its consistency. When the food is liquid or very soft Kronecker 

 and Meltzer have shown that it is shot through the whole length of 

 the esophagus by the force of the initial act of swallowing. It- 

 arrives at the lower end of the esophagus in about 0.1 sec., and may 

 pass immediately into the stomach or may lie some moments in the 

 esophagus according to the conditions of the sphincter guarding 

 the cardiac orifice. When, however, the food is solid or semi- 

 solid, as was shown by Cannon and Moser, it is forced down the 

 esophagus by a peristaltic movement of the musculature. The 

 circular muscles are constricted from above downward by an ad- 

 vancing muscular wave. The upper portion of the esopha- 

 gus contains cross-striated fibers indicating rapid contraction; 

 the lower end consists of plain muscle only, while the intermediate 

 portion is a mixture of the two varieties. Kronecker and Meltzer 

 believe that each of these segments contracts as a whole and in 

 orderly succession, but other observers, on the evidence furnished 

 by Roentgen-ray photographs, agree that there is no perceptible 

 pause in the downward movement of the wave of contraction. These 

 same movements occur in the swallowing of liquid or soft food, but 

 in such cases the peristaltic wave follows the actual descent of the 

 food. According to the observation of Kronecker and Meltzer, it 

 takes about 6 sec. for the peristaltic wave to reach the stomach, 

 and the passage of the food through the cardia takes place with 

 sufficient energy to give rise to a murmur that may be heard by 

 auscultating over this region. In the case of the more liquid food 

 that is shot at once to the lower end of the esophagus, it may 

 apparently pass at once into the stomach or it may lie in the 

 esophagus until the wave of contraction reaches it (6 sec.) and 

 forces it through the opening. According to the observations 

 made by Hertz,* liquids or liquid food are held up at the end 

 of the esophagus and pass slowly into the stomach through the 

 sphincter. He estimates that an interval of from 4.6 to 8.6 

 sec. elapses before the swallowed bolus disappears into the stom- 

 ach, about one-half of this time being occupied by the pas- 

 sage to the bottom of the esophagus and one-half in the tran- 

 sit through the cardiac orifice of the stomach. 



Nervous Control of Deglutition. The entire act of swallowing, 



as has been said, is essentially a reflex act. Even the comparatively 



simple wave of contraction that sweeps over the esophagus is due 



to a reflex nervous stimulation, and is not a simple conduction of 



* Hertz, ''Guy's Hospital Reports," 61, 389, 1907. 



