DIGESTION. 101 



When in feeding animals the kind of food is altered and the new 

 diet maintained for a length of time, it is found that the ferment- 

 content of the juice becomes from day to day more and more adapted 

 to the requirements of the food. If, for example, a dog has been fed 

 for weeks on nothing but milk and bread and is then put on an 

 exclusive flesh diet, which contains more proteid, but scarcely any 

 carbohydrate, a continuous increase of the proteid ferment in the 

 juice is to be observed. The capability of digesting proteid waxes 

 from day to day, while, on the contrary, the amylolytic power of the 

 juice continuously wanes. 



When under the influence of a given diet this or that condition 

 of the pancreas had been established in experiment-animals in char- 

 acteristic form, Pawlow was able, by altering the feeding, to reverse 

 it several times in the same animal. It seems then that the gastric 

 and pancreatic glands have what may be called a form of instinct. 

 They pour out their juice in a manner which exactly corresponds 

 both qualitatively and quantitatively to the amount and kind of food 

 partaken of. Besides, they secrete precisely that quantity of fluid 

 which is most advantageous for the digestion of the meal. 



Hydrochloric acid of gastric juice acts on pro-secretin in the 

 epithelium of duodenal mucous membrane, producing secretin, a 

 hormone 1 which, when absorbed, greatly excites pancreatic secretion. 

 Fats in the stomach retard stomachic secretion, but increase pan- 

 creatic secretion, chiefly by a reflex action through the duodenum, and 

 not from the mucous membrane of the stomach. Sleep does not 

 arrest pancreatic secretion. 



Psychical effect, strong craving for food and water, are common 

 excitants for both gastric and pancreatic secretion. The extractives 

 of meat excite the gastric secretion, while acids and fats excite the 

 pancreas. 



Sodium bicarbonate and alkalies inhibit pancreatic secretion. 



Secretory Nerves of Pancreas. 



In nonnarcotized dogs whose vagus was divided four days pre- 

 viously and whose cardio-inhibitory fibers had lost their irritability, 

 Pawlow irritated the vagus without pain and obtained an increased 

 pancreatic secretion. He found that vasoconstriction of the pan- 

 creatic vessels prevented the action of the vagus on the pancreas, as 

 did compression of the aorta and pain. He also found in the vagus 



1 Hormone is derived from a Greek word, meaning to excite. 



