494 DIGESTION IN THE INTESTINES [CH. XXXII. 



to the pancreas contained in the vagus is avoided. If the blood 

 supply is diminished by stimulation of vaso-constrictor nerves, the 

 secretion is stopped. 



In connection with Pawlow's interesting results, it is desirable to add some more 

 details. The juice was obtained from dogs by stitching the portion of the intestinal 

 wall that contained the orifice of the main pancreatic duct to the abdominal wall, 

 in such a way that the juice was poured to the exterior and could be readily 

 collected. If both vagi are prepared, stimulation of one causes secretion after a 

 latent period which may amount to as much as fifteen minutes. If, then, while the 

 juice is flowing, the opposite vagus is stimulated, the secretion is at once arrested ; 

 this shows the existence of secreto-inhibitory fibres, which it will be remembered is 

 also the case with the stomach. One of the most effective ways of producing a flow 

 of pancreatic juice is to introduce acid into the duodenum, and no doubt the acid 

 gastric juice under normal circumstances is the stimulus for the pancreatic flow. 

 If while the juice so produced is flowing, the vagus is stimulated, partial inhibition 

 occurs in all cases. 



The existence of secretory fibres in the sympathetic for the gastric glands is 

 uncertain, but they certainly are present for the pancreas. 



If the branches of nerves that actually enter the pancreas are stimulated, it is 

 possible to differentiate between the secretory and the inhibitory fibres, for the 

 excitation of some branches give mainly secretion, and of others mainly inhibition. 



We may next compare the pancreatic to the gastric secretion, and we shall see 

 how beautifully adjusted is the mechanism to the work it has to .do. 



The amount of gastric juice rises to a maximum at the end of the first hour, and 

 then slowly falls to zero, which it reaches at the fifth hour after the meal. The 

 pancreatic secretion rises to its maximum when it is most wanted namely, later, 

 i.e.) at the end of the third hour, and falls to zero at the end of the fifth hour. 



The digestive power of the juices varies with the kind of food given. Thus 

 with gastric juice, if the proteolytic activity when milk (a readily digestible food) 

 is given be taken as 1 , that when meat is given is 1^, and when bread is given it 

 rises to 4, the proteid of bread being relatively very insoluble. The total acid 

 secreted is, however, greatest with meat and lowest with bread. 



Using the same three typical foods, the results with pancreatic secretion are as 

 follows : 



When meat is given, a large amount of pancreatic juice is secreted, with medium 

 proteolytic power, and low diastatic and fat-splitting activity. 



When bread is given, more juice is secreted ; its fat-splitting action is very 

 feeble ; its proteolytic power, at first of medium strength, rapidly rises ; and its 

 diastatic action similarly increases quickly. 



When milk is given, the juice first secreted has high proteolytic and diastatic 

 properties ; but these fall gradually, whereas the fat-splitting action is very great. 



The so-called Peripheral Reflex Secretion of the Pancreas. 



We have already seen that the introduction of acid into the duo- 

 denum causes a flow of pancreatic juice. Popielski and Wertheimer 

 and Le Page showed that this flow still occurs when the nerves supply- 

 ing the duodenum and pancreas have been cut through. Wertheimer 

 also mentions that the flow can be excited by injection of acid into 

 the jejunum, but not when it is injected into the lower part of the 

 ileum. These authors conclude that the secretion is a local reflex, 

 the centres being situated in the scattered ganglia of the pancreas, or, 

 in the case of the jejunum, in the ganglia of the solar plexus. 



This subject has been re-investigated by Starling and Bayliss, and 

 the results they have obtained are most noteworthy. They consider 



