158 TEXT-BOOK OF PHYSIOLOGY. 



may be termed the sphincter cardies muscle. By its action it prevents a 

 return under normal conditions of food into the esophagus. 



The deglutitive act may be for convenience divided into three stages, viz. : 



1. The passage of the food from the mouth into the pharynx. 



2. The passage of the food through the pharynx into the esophagus. 



3. The passage of the food through the esophagus into the stomach. 



In the first stage the bolus of food is placed on the superior surface of the 

 tongue. The mouth is then closed and respiration is momentarily sus- 

 pended. The tip of the tongue is placed against the posterior surfaces of the 

 teeth. The tongue, by reason of its intrinsic musculature, then arches from 

 before backward against the roof of the mouth and pushes the bolus of food 

 through the isthmus of the fauces into the pharynx. This completes the 

 first stage. It is a voluntary effort and accomplished partly by the tongue, 

 though, as shown by Meltzer, mainly by the mylohyoid muscles. 



The second and third stages, or the passage of the food through the 

 pharynx and esophagus into the stomach, have been attributed until quite 

 recently entirely to peristaltic movements of their musculature. 1 It has been 

 stated that with the passage of the food through the isthmus of the fauces the 

 posterior wall of the pharynx advances and seizes the food, which, in 

 consequence of a rapid peristaltic movement running through the constrictor 

 muscles from above downward is transferred to the esophagus; that with the 

 entrance of the food into the esophagus a similar peristalsis, varying in rapidity 

 in different sections in consequence of a change in the character of its 

 musculature, gradually transfers the food into the stomach. There can be 

 but slight doubt that by this method the bolus of food, especially if it is of firm 

 consistence and of a size sufficient to distend the esophagus, is transferred 

 into the stomach, but that it is the exceptional rather than the usual method 

 has been demonstrated by Kronecker, Falk, and Meltzer. 



In 1880 the first of these experimenters made the observation that the 

 sensation in the stomach following the swallowing of a mouthful of cold water 

 occurred too quickly to be explained by the prevalent belief that its transfer- 

 ence was caused by ordinary peristalsis, the rate of progression of which was 

 known to be slow. Falk then discovered the fact, by introducing through 

 the mouth into the pharynx a tube connected externally with a water mano- 

 meter, that during the act of swallowing there is a sudden rise of pressure 

 equal to about twenty centimeters of water. 



These experiments demonstrated that at the beginning of deglutition 

 there is a sudden rise of pressure, the result of a quickly acting force resident 

 in the mouth or pharynx, in consequence of which the food is rapidly thrown 

 down into the stomach, peristalsis playing no part in the process. The 

 proof, however, of these statements was furnished by Meltzer. This ob- 

 server introduced into the pharynx and esophagus rubber tubes, the ends of 

 which were provided with thin-walled rubber balloons which could be 

 distended with air. The outer ends of the tubes were connected with 

 Marey's recording tambours. Any compression of the balloon would be 

 followed by the passage of the air into the tambour and an elevation of the 



1 Peristalsis may be defined as a progressive wave-like movement which passes over different 

 portions of the walls of the alimentary canal. Its effect physiologically is the propulsion of its 

 solid and semisolid contents. It is characterized by a contraction of the muscle-fibers behind 

 the object and an inhibition or relaxation of the muscle-fibers in front of it. (Bayliss and Starling.) 



