DIGESTION lg 



Fig 78 is a record of the gastric contractions in man as recorded by the 

 lever of a Marey tambour in connection with a thin rubber sausage-shaped 

 balloon. The balloon was swallowed in the collapsed state and then in 

 flated under a pressure of about eight millimeters of mercury During the 

 experiment which lasted from one to an hour and a half, the subject was 

 placed in the recumbent position and frequently fell asleep The abdomen 

 was auscultated for sounds of peristalsis in the intestine. The passage of 

 food from the stomach into the duodenum was easily heard and coincided 

 with a fall of intragastric pressure as recorded in the tracing 



The conditions necessary for the development of the gastric peristalsis 

 are (i) a condition of tonicity of the musculature, i.e., a slight degree of con- 

 traction whereby the muscle is shortened; (2) intragastric pressure. When 

 these two conditions are mutually adapted the musculature acquires a cer- 

 tain degree of tension whereupon the peristalsis arises. An excess or de- 



FIG. 78. GASTRIC CONTRACTIONS DURING DIGESTION. (Two hours after eating.) 

 The upper tracing shows respiratory excursions, the variation in the bases of which records the 

 changes in intragastric pressure. The heavier markings at the bases of the respiratory tracings 

 are heart-beats. Time marked in minutes. Analysis of the gastric contractions divides them into 

 long tonus waves of about 60 to 90 seconds duration, superposed upon which are shorter peristaltic 

 waves about 20 seconds in duration. 



The lower tracing shows gastric digestive contractions with heart-beats, taken while holding the 

 breath at the end of an expiration. The intervals represent periods of respiration during which the 

 pen was removed from the drum. Were the intervals connected, a regular sequence of gastric tonus 

 waves with peristaltic waves superposed would appear. 



ficiency of internal pressure as well as a loss of tonicity prevents peristalsis. 

 The peristalsis has no necessary fixed point of origin but arises at that 

 portion of the stomach in which the two factors previously mentioned bear 

 a certain relation one to the other. From their origin the peristaltic waves 

 pass toward the pylorus as a result of increased internal pressure. The 

 necessary degree of the preliminary tonus is imparted to the musculature 

 by nerve impulses descending the vagi. If these nerves are cut, the tonus is 

 impaired and peristalsis fails to develop. After a variable period the neuro- 

 muscular mechanism develops a tonus like that given to it by the vagi, after 

 which' the usual peristalsis returns. When once the peristalsis is well devel- 

 oped in digestion, division of the vagi has no effect. (Cannon.) 



The Nerve Mechanism of the Stomach. In preceding paragraphs 

 it was stated that during the period of gastric digestion the food is retained 



