744 PHYSIOLOGY 



The part thus cut off then diminishes in size in every direction, part of its 

 contents being forced through the pyloric canal, while the remainder escapes 

 back as an axial reflux stream into the stomach. The waves recur at regular 

 intervals of fifteen to twenty seconds, and three or four are present simul- 

 taneously. They continue without cessation until the stomach is empty 

 from one to four hours after the meal according to its bulk and composition. 



The foregoing descriptions apply especially to the events which succeed 

 the taking of a considerable meal. If warm fluid alone, e. g. water, be swal- 

 lowed, the opening of the pylorus occurs within a very short time after 

 the fluid has reached the stomach. Thus if a large draught of water be taken 

 to quench thirst, it may arrive in the duodenum within a minute or two after 

 being swallowed, and it is from the duodenum and small intestine that any 

 absorption takes place. When a meal is undergoing digestion, there is a dis- 

 tinct relation between the amount of acid present in the gastric contents and 

 the opening of the pylorus. One may indeed say that acidity of the gastric 

 contents exercises a direct inhibitory stimulus on the pyloric sphincter. 



These movements of the two portions of the stomach may be observed 

 also on anaesthetised animals and even on a stomach which has been excised 

 and placed in warm salt solution. They must therefore have their origin in 

 the walls of the stomach itself. Although the co-ordination between the two 

 parts of the stomach, between the tonic contractions of the fundus and the 

 rhythmic contractions of the pyloric part, may be carried out by the local 

 nervous system Auerbach's plexus situated between the layers of the 

 muscular coat, it is probable that the advancing waves of contraction 

 observed in the antrum are myogenic, i. e. directly originated in and deter- 

 mined by the muscle fibres themselves. Cannon has shown that these 

 movements persist after complete division of Auerbach's plexus by 2 to 6 

 circular incisions carried through the entire muscular coat of the stomach ; 

 and it is evident that they do not partake of the nature of a true peristalsis, 

 since they are not preceded by a wave of relaxation. The opening of the 

 pylorus, on the other hand, which occurs at increasingly frequent intervals 

 at the -end of a wave, must be ascribed to a nervous mechanism. Although 

 the local mechanism probably plays the greater part in this act of relaxation, 

 the normal emptying of the stomach is also largely dependent on the integrity 

 of the connection of this viscus with the central nervous system. If both 

 vagus nerves be divided in a dog below the point at which they give off their 

 branches to the lungs and heart, a large amount of food may remain in 

 the stomach in an undigested condition. The secretion of gastric juice is 

 deficient, and the opening of the pylorus is not easily carried out. Such dogs 

 therefore tend to die of saprscmia, being poisoned by the absorption of 

 products of putrefaction from the gastric contents. Pawlow has shown that 

 animals can be kept alive for months after division of both vagi if a gastric 

 fistula be made, the animals be carefully fed, and care be taken to wash out 

 adherent non-digested portions of food from the stomach. 



The opening of the pylorus depends not only on intragastric events but 

 also on the condition of the duodenum. It has been shown by Serdjukow 



