I NFL UENCE OF NER VO US S YSTEM ON DIGESTI VE GLANDS 409 



water stimulate the pancreatic secretion, and with great promptness, 

 even before any acid has been produced in the stomach, and there- 

 fore before any can have passed into the duodenum. Possibly this 

 effect is elicited through the long reflex paths already described as 

 running in the vagi or through a local nervous mechanism, which, 

 although it does not take part in the excitation of the pancreatic 

 secretion by acid, may yet exist for the performance of other offices. 

 It is more probable, however, that it is due to the passage of some of 

 the gastric contents through the pylorus; for when oil is introduced 

 into the small intestine, it causes the production of secretin, although, 

 unlike dilute acid, it is quite ineffective in forming secretin when 

 rubbed up with the scraped-off mucous membrane. That secretin 

 acts on the pancreatic cells in a different way from the secretory 

 nerve fibres contained in the vagus is indicated by the difference in 

 the characters of the juice secreted under the influence of the two 

 mechanisms. The nervous secre- 

 tion is thick and opalescent, rich 

 in enzymes, including trypsin in 

 the active form, and proteins, but 

 its alkali content is low. Like 

 other secretions excited through 

 nerves, it is inhibited by atropine. 

 The chemical secretion due to 

 secretin, is thin and watery, rich Fi - 166. Rate of Secretion of Pan- 



n v j creatic Juice. S shows the variation 



in alkalies, poor in proteins and in the r j ate o{ secretion of the pan . 



in enzymes, and among the latter, creatic juice in a dog; P, the varia- 



trypsin occurs only in the inactive tion in the percentage of solids in 



/c ., , x the juice. It will be seen that the 



n ^awitSCnj. < maxima of S fall at the same time 



The pancreatic, like the gastric, as the maxima of P. The numbers 



juice is said to vary as regards alon S the horizontal axis are hours 



j-. _, / ,T~ ,-u since the last meal, 

 its digestive properties with the 



nature of the food. On a diet of bread the juice is very poor 

 in fat-splitting ferment, while on a diet of flesh it is richer, and 

 on a diet of milk richest of all. With bread the juice is relatively 

 rich in amylolytic ferment. When we take the quantity of the 

 juice as well as its strength in ferments into consideration, it is 

 stated that bread occasions the secretion of a juice with a greater 

 quantity of proteolytic ferment than either milk or meat, although 

 it is relatively dilute (Fig. 169). The vegetable proteins require 

 more ferment to digest them than proteins of animal origin. * There 

 is no more evidence that the adaptation of the pancreatic juice to the 

 nature of the food is due to a specific sensibility of the duodenal 

 mucosa to the various food-stuffs than there is in the case of the 

 adaptation of the gastric juice. If the volume of the chyme and its 

 acidity are related to the nature of the food, then the amount of 

 secretin formed, and therefore the intensity of secretion in the 



