406 



DIGESTION 



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probably connected with a reflex centre in the medulla oblongata. 

 It has long been known that when the medulla is stimulated a flow 

 of pancreatic juice is occasionally set up, or is increased if already 

 going on. The same is true when the vagus is stimulated in the 

 ordinary way in the neck. But the experiment often failed, for 



the pancreas 

 is peculiarly 

 susceptible 

 to circulatory 

 disturbances, 

 and stimula- 

 tion of the 

 bulb or the 

 vagus may 

 interfere with 

 the blood- 

 flow through 

 the gland by 

 exciting its 

 vaso-con- 



strictor fibres or causing inhibition of the heart. These disturbing 

 influences may be avoided, as Pawlow has shown, by stimulating the 

 vagus, three or four days after dividing it, with slowly-recurring 

 stimuli (induction shocks or light blows from a small hammer 

 worked by an 



Flesh, 200 grm. 



Bread, 200 grm. 



Milk, 600 c.c. 



Fig. 163. Rate of Secretion of Gastric Juice with Diets of Meat, 

 Bread, and Milk (Pawlow). 



excitable, and the vaso-constrictors are but little affected by 

 these slow rhythmical stimuli, which excite the secretory nerves 

 (p. 175). A pancreatic fistula has previously been established by 

 excising a small portion of the duodenal wall containing the open- 

 ing of the pancreatic duct, closing the intestine by sutures, and 



