204 DIGESTION". 



united into a single bolus, it slips easily from the back, of the 

 tongue along the membrane covering the anterior and infe- 

 rior part of the pharynx ; but if it be liquid or of little consist- 

 ence, a portion takes this course, but another portion passes 

 over the epiglottis, being directed by it into the two grooves 

 or gutters by the side of the larynx. 



It is by these means, together with those by which the 

 posterior nares are protected, that all solids and liquids are 

 directed to the oesophagus, and the second period of degluti- 

 tion is safely accomplished. 



The third period of deglutition is the most simple of all. 

 It involves merely contractions of the muscular walls of the 

 oesophagus, by which the food is forced into the stomach. 

 The longitudinal fibres shorten the tube and slip the mucous 

 membrane, lubricated by its glairy secretion, above the 

 bolus ; while the circular fibres by a progressive peristaltic 

 contraction from above downward strip the food, as it were, 

 into the stomach. This shortening of the tube was well 

 illustrated in an observation on a female suffering under a 

 gastric fistula, by Halle ; who noted a protrusion of the mu- 

 cous membrane which naturally undergoes no shortening 

 into the stomach with each act of deglutition. 1 The passage 

 of food down the oesophagus was for the first time closely 

 studied by Magendie ; who noted, in this connection, many 

 curious and important facts. In numerous experiments on 

 the lower animals, he observed that while the peristaltic 

 contractions of the upper two-thirds of the tube were imme- 

 diately followed by a relaxation which continued till the 

 next act of deglutition, the lower third remained contracted 

 generally for about thirty seconds after ^ the passage of the 

 food into the stomach. During its contraction, this part of 

 the oesophagus was hard, like a cord firmly stretched. This 

 was followed by relaxation ; and this alternate contraction 

 and relaxation continued constantly, even when the stomach 



1 MAGENDIE, Precis filemeniaire de Physiologie, Paris, 1836, tome ii., p. 69. 



