1 84 DIGESTION 



traction and relaxation continue, even when the stomach is empty, 

 although, during digestion, the contractions are frequent in proportion 

 to the quantity of food in the stomach. The contraction is always 

 increased by pressing the stomach and attempting to pass some of its 

 contents into the oesophagus. This provision is important in prevent- 

 ing regurgitation of the contents of the stomach, especially when the 

 organ is exposed to pressure, as in urination or defecation. 



An approximate estimate of the duration of the acts of deglutition is 

 given in the following quotation from Landois : 



" According to Meltzer and Kronecker, the duration of deglutition 

 in the mouth is 0.3 second ; then the constrictors of the pharynx con- 

 tract 0.9 second ; afterward, the upper part of the oesophagus ; then 

 after 1.8 second, the middle; and after another 3 seconds, the lower 

 constrictor. The closure of the cardia, after the entrance of the bolus 

 into the stomach, is the final act in the total series of movements." 



A complete act of deglutition occupies about six seconds. The first 

 act usually is automatic but is under the control of the will. The 

 second act is involuntary when once begun, but it 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 unless 

 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 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 repeated, the move- 

 ments become impossible, until time enough has elapsed between them 

 for the saliva to collect. 



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. I have seen a juggler pass a pint of liquid from the 

 mouth to the stomach, while standing on his hands. 



It is not very uncommon to find persons who have gradually acquired 

 the habit of swallowing air in order to relieve uncomfortable sensations 

 in the stomach; and when confirmed, this practice occasions persistent 

 disorder in digestion. A number of cases of this kind were 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 was observed by the late Dr. Austin Flint and is reported 

 in his work on the Practice of Medicine. 



