162 TEXT-BOOK OF PHYSIOLOGY 



passage of the bolus, the second, B, due to the compression exerted by the 

 contraction of the pharyngeal muscles. The interval of time between these 

 two crests amounts to not more than 0.3 second. In the esophageal curve, 

 3, the elevation, C, corresponds to the elevation, A, and is likewise due to 

 the compression exerted by the bolus. The interval of time between the 

 beginning of the first and second curves was not more than o.i second, 

 regardless of the depth to which the esophageal balloon was plunged. At a 

 later period a second rise of the lever was recorded; the time of its appear- 

 ance, height, duration, etc., were found to increase with the depth of the 

 balloon. 



These facts demonstrate that deglutition consists of two phases: (i) a 

 rapid rise of pressure in the pharynx, as a result of which liquid or semi- 

 liquid foods are suddenly shot down to the lower end of the esophagus; (2) 

 a peristaltic contraction of the musculature of the canal, which, acting as a 

 supplementary force, carries onward any particles of food in the canal 

 and forces the bolus through the closed sphincter cardice at the end of the 

 esophagus. 



The immediate cause of the sudden rise, of pressure was shown by 

 Meltzer to be the contraction of the mylohyoid muscles. When the nerves 

 abolishedthese muscles were divided in a dog, deglutition was practically 

 going to . These muscles are probably assisted in their action by the 

 contraction of the hyoglossus muscles as well as the tongue itself. 



The time required for a mouthful of liquid food to pass to the lower end 

 of the esophagus is approximately about o.i second. If the cardiac orifice 

 is normally closed, a period of about 6 or 7 seconds may elapse before the on- 

 coming peristaltic wave reaches the end of the esophagus and forces the 

 fluid into the stomach. If, however, a series of deglutitory acts follow one 

 another in quick succession there is an inhibition of the cardiac sphincter and 

 the peristaltic wave until after the last swallow. The time required for the 

 food to pass down the esophagus and into the stomach may vary in different 

 animals and in different human beings. 



An examination of the action of the esophagus during deglutition, made 

 by Cannon and Moser with x-rays and the fluoroscope, disclosed the fact 

 that the method of food transmission varied in different animals. In the 

 cat and dog the transmission was effected by peristalsis alone. The time 

 required for the food to reach the stomach varied in the cat from nine to 

 twelve seconds and in the dog from four to five seconds. The descent of 

 the bolus was more rapid in the upper than in the lower part of the esophagus. 

 In man, liquids descended rapidly, at the rate of several feet a second, in 

 consequence of the rapid and energetic contraction of the mylohyoid muscles. 

 A peristaltic contraction, passing over the entire esophagus, was necessary 

 to the passage of solid and semisolid food through it. 



Closure of the Posterior Nares and Larynx. Because of the rapid 

 rise of pressure in the deglutitory canal during the act of swallowing it is 

 essential that the openings into the nasal and laryngeal cavities be closed to 

 prevent the entrance of food into them, which would otherwise take place. 

 Under normal circumstances this is done so effectually that it is seldom that 

 any portion of the food, liquid or solid, ever enters the nasal chambers 

 or the cavity of the larynx. The mechanism by which these openings are 

 closed is as follows: 



