i82 TEXT-BOOK OF PHYSIOLOGY 



3. The Movements of the Cardiac Portion. As digestion proceeds, the pre- 

 vestibular or cardiac portion of the stomach elongates and assumes the shape 

 of a tube, which becomes the seat also of peristaltic constriction waves. As 

 a result, some of the food is gradually forced into the pyloric region to succeed 

 that which has been prepared and ejected into the duodenum. As the pre- 

 vestibular tube is emptied of its contents the longitudinal and circular fibers 

 of the fundus steadily contract and gradually force its contents into the 

 tubular portion. This continues until the fundus is completely emptied. 

 The changes in shape which the cardiac portion undergoes during digestion 

 are represented in Fig. 74. The fundus acts as a reservoir for the food and 

 forces out its contents a little at a time as the vestibular mechanism is ready 

 to receive them. Since peristaltic movements are absent from the fundus 

 portion, the food is not mixed with gastric juice, and therefore salivary diges- 

 tion can continue for a considerable period. There is no evidence of a circu- 

 lation of food in the stomach as sometimes described. On the contrary, the 

 movement through the elongated tube is in general a progressive though an 

 oscillating one. As the constriction waves rapidly pass over the food it is 

 advanced toward the pyloric orifice, but as this is closed the food is forced 

 backward through the advancing constricted ring for a variable distance. 



The effect of the constriction waves is to mix the food with the gastric 

 juice, triturate and soften it. So soon as this is effected, the pyloric orifice 

 opens, when the advancing constriction wave expels it into the intestine. 

 With its expulsion, room is afforded for an additional quantity of food, and 

 hence there is a general advance of the food mass toward the pylorus. 



Though these observations were made on the cat, evidence is accumu- 

 lating which goes to show that in human beings the walls of the stomach 

 exhibit constriction waves which are similar in all respects to those above 

 described. Evidence of this character has been furnished by experiments 

 conducted in the author's laboratory by Spencer and Meyer. 



Fig. 76 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- 

 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. Tf these nerves are cut, the tonus is 



