740 PHYSIOLOGY 



certain amount of gastric juice containing both hydrochloric acid and 

 pepsin. In order to produce this positive effect, it was necessary to employ 

 pyloric mucous membrane, extracts made by infusing or boiling cardiac 

 mucous membrane with any of these substances being without effect. 

 Edkins concludes therefore that the secondary secretion of gastric juice is 

 determined, not, as Pawlow and Popielski imagined, by a local stimulation 

 of the reflex nervous apparatus in the gastric wall, but by a chemical 

 mechanism. The first products of digestion act on the pyloric mucous 

 membrane, and produce in this membrane a substance which is absorbed into 

 the blood stream, and earned to all the glands of the stomach, where it acts 

 as a specific excitant of their secretory activity. This substance may be 

 called the gastric secretin or gastric hormone. It is noteworthy that it is 

 produced in that portion of the stomach where the process of absorption is 

 most pronounced. 



The normal gastric secretion is therefore due to the co-operation of two 

 factors. The first and most important is the nervous secretion, determined 

 through the vagus nerves by stimulation of the mucous membrane of the 

 mouth, or by the arousing of appetite in the higher parts of the brain. The 

 second factor, which provides for the continued secretion of gastric juice 

 long after the mental effects of a meal have disappeared, is chemical, and 

 depends on the production in the pyloric mucous membrane of a specific 

 substance or hormone, which acts as a chemical messenger to all parts of the 

 stomach, being absorbed into the blood and thence exciting the activity of 

 the various secreting cells in the .gastric glands. It is still a moot point 

 whether this gastric hormone is formed only in the pyloric mucous membrane, 

 or whether it may not be also produced in the lower sections of the gut. 

 Popielski has stated that the introduction of bouillon into the small intestine 

 excites a secretion of gastric juice in animals, even after extirpation of the 

 abdominal sympathetic plexuses and division of both vagi. On the other 

 hand, introduction of the same substance into the large intestine has no 

 influence on gastric secretion. Popielski ascribes this secretion again to a 

 local reflex ; but it is more probable that the mechanism in this case is the 

 same as that involved in the secretion which is excited by the presence of 

 semi-digested food in the stomach itself. 



Pawlow has shown that the second phase of the gastric secretion is largely 

 influenced by the character of the contents of the stomach. Thus the inges- 

 tion of large quantities of oil diminishes considerably the amount of gastric 

 juice secreted, and Pawlow has suggested the administration of oil or oily 

 foods as a possible remedy in cases where the production of gastric juice, 

 and especially of hydrochloric acid, is in excess. It has long been imagined 

 that the secretion of gastric juice was stimulated by the taking of alkalies. 

 This idea has been shown by Pawlow to be erroneous. Whereas the forma- 

 tion of gastric juice is increased by the administration of acids, especially 

 after a meal, it is largely diminished by the administration of alkalies such 

 as sodium bicarbonate. In fact, sodium bicarbonate diminishes the activity 

 of the digestive glands throughout the alimentary tract, and can be used as 



