780 PHYSIOLOGY 



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 nhicous 

 membrane of the mouth, or by the arousing of appetite in the higher 

 parts of the brain. The second factor, which provides for the con- 

 tinued 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 extir- 

 pation 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 ingestion 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 formation 

 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 a means of diminishing the secretion of gastric 

 juice as well as of pancreatic juice. 



A further important question has been propounded by Pawlow, 

 namely, whether there is any alteration in the constitution and 

 amount of gastric juice with variations in the character of the food. 

 So far as concerns the first phase of secretion, the psychical or ' appetite' 

 juice, this observer has shown that, whatever the previous diet of 



