338 HUMAN PHYSIOLOGY 



It has thus been found that (1) The amount of secretion 

 depends upon the amount of food taken. (2) The amount 

 and course of secretion varies with the kind of food taken. 

 Thus, with flesh the secretion reaches its maximum at the end 

 of one hour, persists for an hour and then rapidly falls, while 

 with bread it reaches its maximum at the end of one hour, 

 rapidly falls but persists for a much longer period than in 

 the case of flesh. (3) The digestive activity of the juices 

 varies with the kind of food and with the course of diges- 

 tion. It is higher and persists longer after a diet of bread, 

 which is difficult to digest, than after a diet of flesh, which is 

 more easily digested. (4) The percentage of acid does not 

 vary markedly. When more acid is required more gastric 

 juice is secreted. (5) The work done by the gastric glands is 

 greater in the digestion of bread than in the digestion of 

 flesh. 



(g) Nervous Mechanism of Gastric Secretion. It has 

 been proved that in the dog the secretion of gastric juice can 

 go on after the nerves to the stomach have been divided, and 

 this has been ascribed to a reflex stimulation of the nerve 

 plexus in the submucosa. But while this is the case, the 

 vagus also exercises a direct influence. This was proved by 

 experiments on dogs in which Pawlow's pouch had been 

 made, and in which the oesophagus was opened in the 

 neck, so that when food was taken it did not pass into the 

 stomach. It was found that letting the dog swallow food, 

 which of course escaped by the opening in the oesophagus, 

 or merely showing food to the dog, caused a secretion of 

 gastric juice if the vagi were intact, but not after they were 

 divided. 



3. Movements of the Stomach. These have been studied 

 by feeding an animal with food containing bismuth, and then 

 applying X rays, which are intercepted by the coating of 

 bismuth, so that a shadow picture of the shape of the 

 stomach is given (Fig. 149). 



It is found that, soon after food is taken, a constriction 

 forms about the middle of the stomach and slowly passes on 

 towards the pylorus. Another constriction forms and follows 

 the first, and thus the pyloric part of the stomach is set into 



