80 PHYSIOLOGY. 



kinds of proteid receive, therefore, quantities of ferment correspond- 

 ing to the differences in their digestibility, which we already know 

 from experiments in physiological chemistry. 



Excitants of Flow of Gastric Juice. 



Before the dog adapted for sham feeding, Pawlow cut up meat 

 and sausage, when he obtained a great flow of gastric juice, more so 

 than when he fed the dog with them ; they escaped by the oesophagus. 

 Here is a psychic excitation of the gastric secretion, which plays a 

 considerable part in the production of gastric juice in the sham feed- 

 ing experiment. 



The appetite is, then, the first and mightiest exciter of the secre- 

 tory nerves of the stomach. A good appetite in eating is equivalent 

 from the outset to a vigorous secretion of the strongest gastric juice. 

 Sham feeding of five minutes does not call forth a secretion for longer 

 than three to four hours. 



Mechanical excitation of the mucous membrane of the stomach 

 does not cause the flow of gastric juice. Sodium bicarbonate in the 

 stomach inhibits its secretion. Liebig's extract or meat-broth intro- 

 duced into the stomach increases the secretion of gastric juice. Fat 

 in the stomach inhibits the psychic secretory action of the stomach 

 upon meat. The fat of milk can inhibit its digestion to a certain 

 extent. 



The secretory activity of the stomach depends on nervous pro- 

 cesses. In the immense majority of cases gastric digestion begins by 

 a strong central excitation of the secretory and trophic fibers of the 

 glands. 



Popielski has shown that a stomach with all nervous connections 

 severed will secrete gastric juice, if extracts of meat are placed in the 

 stomach. Edkins believes this secondary secretion of gastric juice 

 to be due to the action of the products of digestion on the pyloric 

 mucous membrane. They produce in the membrane a chemical sub- 

 stance, which is absorbed into the circulation, and, conveyed to the 

 glands of the stomach, it acts as a specific excitant of their secretory 

 activity. Starling calls it a gastric secretion or gastric hormone, 

 similar to the secretin-exciting pancreatic secretion. 



Secretory Nerves of the Stomach. 



In a dog with a cannula in the stomach and the oesophagus 

 opened so that food leaving the mouth goes through the opening in 

 the oesophagus, and not into the stomach ("sham feeding"), the swal- 



