SECRETION OF PANCREATIC JUICE 



271 



Hours 123123 



nerves of the small intestine. It could be pointed out in support of this view 

 that injection of acids into the rectum or directly into the blood evoked no secre- 

 tion, and that therefore the glands could not be stimulated from the blood. Bay- 

 liss and Starling, however, observed that an extract of the intestinal mucous 

 membrane with HC1, injected into a 

 vein, called forth the pancreatic secre- 

 tion at once. The acid dissolves out of 

 the mucous membrane a substance, not 

 destroyed by boiling and called by the 

 authors secretin, which in their opinion 

 acts specifically upon the pancreas and 

 constitutes the only natural cause of its 

 secretory activity. 



Beyond all doubt secretin is a pow- 

 erful excitant of the pancreatic secre- 

 tion; but its specific nature is denied 

 by several authors. Since, however, CO, 

 from the small intestine also produces a 

 flow of pancreatic juice, and there is 

 of course no secretin extract of the 

 mucosa in this; since, further, the acid 

 introduced into an intestinal loop has 

 an exciting action on the pancreas, even 

 when the venous blood of this loop is 

 diverted and the thoracic duct is tied 

 off, one is justified in the assumption 

 that on introduction of acid into the in- 

 testine the secretion is produced partly 

 by a reflex set up by the acid, and partly 

 through the secretin in the blood. 



Nothing definite can be said con- 

 cerning the nerve centers of pancreatic 

 secretion. The observations which pur- 

 ported to demonstrate reflex centers in the gland itself are no longer convincing 

 since the discovery of secretin. 



The hourly course of the secretion, which appears to be connected with 

 variations in the discharge of the stomach contents into the intestine, as well 

 as the amount of the different enzymes present in the secretion, shapes itself 

 according to the food ingested, as may best be seen from the diagrams in 

 Figs. 107 and 108. 1 



From these diagrams it is evident that the absolute rate of secretion fol- 

 lowing milk is different from that following the ingestion of meat and bread ; 

 that the content of amylolytic enzyme is considerably greater for bread than 

 for meat and milk, and that the content of steapsin is much greater for milk 

 than for meat and bread. 



The total quantity of nitrogen which is given off in the pancreatic juice 

 during a period of digestion varies much with different foods. In fact with the 



1 With regard to Fig. 108 it should be said that the observations there represented 

 were made before the discovery of enterokinase, and give therefore only the manifest 

 trypsin content of the juice. 



18* 



Meat. 



Bread. 



Milk. 



FIG. 108. The enzymes of panceratic juice, 

 after feeding exclusively with meat, with 

 bread and with milk, after Walther. 



