DEGLUTITION. 225 



can soon be recognized in the stomach by their temperature. As the lower part of the 

 oesophagus is composed chiefly of unstriped muscular fibres, it is probable that here the 

 contractions are more gradual than in the upper portions. 



As we have already had occasion to remark, the muscular movements which take place 

 during all the periods of deglutition are peculiar. The first act is generally involuntary from 

 inattention, but it is under the control of the will. The second act is involuntary when 

 once commenced, but may be excited by the voluntary passage of solids or liquids beyond 

 the velum pendulum palati. It is impossible to perform the second act of deglutition un- 

 less there be some article, either solid or liquid, in the pharynx. It is easy to make three 

 or four successful efforts consecutively, in which there is elevation of the larynx with all 

 the other characteristic movements ; but a little attention will show that with each act 

 a small quantity of saliva is swallowed. When the efforts have been frequently repeat- 

 ed, the movements become impossible, until time enough has elapsed between them for 

 the saliva to collect. This fact we personally verified before writing this paragraph, 

 and it was demonstrated to be due to the absence of liquid ; for, immediately after, an 

 ounce of water was swallowed without difficulty by sixteen successive movements of 

 deglutition. This experiment also shows the small quantity of liquid (only half a drachm) 

 necessary to excite the contraction of the muscles concerned in the second act. 



All the movements of deglutition, except those of the first period, must be regarded as 

 essentially reflex, depending upon an impression made upon the afferent nerves distrib- 

 uted to the mucous membrane of the pharynx and oesophagus. 



The position of the body has little to do with the facility with which deglutition is 

 effected. Liquids or solids may be swallowed indifferently in all postures. Berard states 

 that a juggler, in his presence, passed an entire bottle of wine from the mouth to the 

 stomach, while standing on his head. The same feat we have lately seen accomplished 

 with apparent ease, by a juggler who drank three glasses of beer while standing on his 

 hands in the inverted posture. 



Deglutition of Air. In the celebrated essay of Magendie on the mechanism of vom- 

 iting, it is stated that as soon as nausea commenced the stomach began to fill with air, so 

 that, before vomiting occurred, the organ became tripled in size. Magendie showed, far- 

 therm ore, that the air entered the stomach by the oesophagus, for the distention occurred 

 when the pylorus was ligated. In a subsequent memoir, the question of the deglutition 

 of air, aside from the small quantity which is incorporated with the food during mastica- 

 tion and insalivation, was farther investigated. It was found that some persons had the 

 faculty of swallowing air, and, by practice, Magendie himself was able to acquire it, 

 although it occasioned such distress that it was discontinued. Out of a hundred students 

 of medicine, eight or ten were found able to swallow air. 



It is not very uncommon to find- persons who have gradually acquired this habit in 

 order to relieve uncomfortable sensations in the stomach ; and, when -confirmed, it occa- 

 sions persistent disorder in the process of digestion. Quite a number of cases of this 

 kind are reported by Magendie, and in several it was carried to such an extent as to pro- 

 duce great distention of the abdomen. A curious case of habitual air-swallowing is re- 

 ported by Dr. Austin Flint, in his work on the Practice of Medicine. 



Although the subject of air-swallowing properly belongs to pathology, the fact that 

 the muscles of deglutition are capable, in some individuals, of forcing air into the stom- 

 ach, is not without physiological interest. 



15 



