340 FOOD AND DIGESTION 



contract, the bolus of food is put under great pressure and shot backward and 

 downward through the pharynx and into the esophagus and, if the food be 

 fluid enough, even to the cardiac orifice of the stomach. Coincidently with 

 the contraction of the mylo-hyoid muscles, the hyoglossi are thrown into 

 action, drawing the tongue backward and downward, not only increasing 

 the pressure upon the food, but forcing the epiglottis over the glottis, closing 

 the larynx. 



It has been shown by the Roentgen-ray method that the character of the 

 food determines somewhat its passage through the esophagus. The dry 

 and semisolid foods are seized by the musculation of the esophagus and 

 passed down that organ by a peristaltic wave. The longitudinal muscles 

 contract, tending to enlarge the diameter of the esophagus in advance of the 

 food, while contractions of the circular muscles produce pressure on the 

 bolus just behind, thus forcing it along to the cardia. This wave reaching 

 the cardiac orifice about six seconds after the commencement of the act of 

 deglutition, forces the food into the stomach, the sphincter having previously 

 relaxed. The interval of time between the commencement of the act of 

 deglutition and the arrival of the more fluid food at the cardiac orifice of the 

 stomach may not be more than one-tenth second, though it remains at the 

 cardiac orifice without entering the stomach until the first parts of the act of 

 swallowing is reinforced by the subsequent contraction of the constrictors of 

 the pharynx and the passage of a peristaltic wave down the esophagus. In 

 some cases, however, the liquid food is not stopped at the cardiac orifice, 

 but is sent through the relaxed sphincter by the original force of the mylo- 

 hyoid contraction. 



In man the esophagus was said to contract in three separate segments, 

 the first segment lying in the neck and being about six centimeters long, the 

 second being the next ten centimeters of the tube, and the third the re- 

 maining portion to the stomach. But the later Roentgen-ray observations 

 show no break in the continuous passage of the food, though the movement 

 of the food is slower in the lower segment of the esophagus. 



The act of swallowing consists, then, of the contraction in sequence of 

 the mylo-hyoids, the constrictors of the pharynx, and of the esophagus. The 

 computed time of contraction is as follows: 



Seconds. 

 Contraction of mylo-hyoids and constrictors of the pharynx ... 0.3 



Contraction of the first part of the esophagus 0.9 



Contraction of the second part of the esophagus 1.8 



Contraction of the third part of the esophagus 3.0 



6.0 



If a second attempt at swallowing be made before the first has been com- 

 pleted (that is, before six seconds have elapsed), the remaining portion of the 



