378 



A MANUAL OF PHYSIOLOGY 



gastric fistula in the older) causes a liquid with the properties of 

 gastric juice to gather in the stomach. This power, then, is a 

 congenital one. The individual does not gain it by experience ; 

 it comes into the world with him (Cohnheim). 



The Influence of Nerves on the Pancreas. Like the stomach, 

 the pancreas receives secretory fibres through the vagus. These 

 are 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 s u s- 

 ceptible to circu- 

 latory disturb- 

 ances, and stimu- 

 lation of the bulb 

 or the vagus may 

 interfere with 

 the blood - flow 

 through the gland 

 by exciting its 

 vaso - constrictor 

 fibres or causing 

 inhibition of the 

 heart. These dis- 

 turbing influ- 

 ences may be 

 avoided, as Paw- 

 low 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 electro-magnet 

 at the rate of about one in the second) . The secretory fibres are 

 still susceptible of excitation, while the cardio-inhibitory fibres, 

 which degenerate more rapidly, are almost or altogether inex- 

 citable, and the vaso-constrictors are but little affected by these 

 slow rhythmical stimuli, which excite the secretory nerves 

 (p. 159). A pancreatic fistula has previously been established 

 by excising a small portion of the duodenal wall containing the 



FIG. 148. SECRETION OF PEPSIN. 



C shows the quantity of pepsin(ogen) in the mucous 

 membrane of the cardiac end of the stomach at different 

 times during digestion ; P, the quantity of pepsin(ogen) in 

 the mucous membrane of the pyloric end ; S, the quantity 

 of pepsin in the secretion of the cardiac glands. The 

 numbers marked along the horizontal axis are hours since 

 the last meal. About five hours after the meal, S reaches 

 its maximum. From the very beginning of the meal C falls 

 steadily down to the tenth hour, and then begins to rise 

 i.e., the gland-cells of the cardiac end of the stomach 

 become poorer in pepsin(ogen) as secretion proceeds. 



