MOVEMENTS OF THE ALIMENTARY CANAL. 637 



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, while the longitudinal muscles contract 

 probably somewhat in advance of this wave so as to dilate the tube 

 and facilitate the passage of the bolus. The upper portion of the 

 esophagus 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 stomach within 0.1 sec, 

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

 lower end of the esophagus until the wave of contraction reaches 

 it (6 sec.) and forces it through the opening. At this opening, the 

 cardia or cardiac orifice, the circular layer of muscles acts as a 

 sphincter which is normally in a condition of tone, particularly 

 when the stomach contains food. The advancing wave of con- 

 traction in the esophagus either forces the food through the resis- 

 tance offered by this sphincter or probably the sphincter suffers 

 an inhibition at this moment as a part of the general reflex action. 

 Kronecker and Meltzer have noted the interesting fact that if a 

 second swallow is made within an interval of six seconds after the 

 first, the peristaltic wave occasioned by the latter is inhibited at 

 whatever portion of its path it may have reached. The food carried 



