SEC. 4. THE SECRETION OF PANCREATIC JUICE 



AND OF BILE. 



§ 213. Tlie Secretion of Pancreatic Juice. Although in some 

 cases, as that of the parotid of the sheep, the flow of saliva is 

 continuous or nearly so, in most animals, as in man, the inter- 

 mittence of the secretion is very nearly absolute. While food is 

 in the mouth saliva Hows freely, but between meals only just 

 sufficient is secreted to keep the mouth moist, and probably the 

 greater part of this is supplied not by the larger salivary but by 

 the small buccal glands. The flow of pancreatic juice, on the 

 other hand, is much more prolonged, being in the rabbit continu- 

 ous, and in the dog lasting for twenty hours after food. But this 

 contrast between the secretion of saliva and that of pancreatic 

 juice is natural, since the stay of food in the mouth even during 

 a protracted feast is relatively short, whereas the time during 

 which the material of a meal is able in some wav or other to affect 

 the pancreas is very prolonged. 



The flow though continuous, or nearly so, is not uniform. In 

 the dog the flow of pancreatic juice begins immediately after food 

 has been taken, and rises to a maximum which may be reached 

 within the first, or as in the case furnishing the diagram given in 

 Fig. 83 the second hour, but which more commonly is not reached 

 until the third or fourth hour. This rise is then followed by a 

 fall, after which there is a secondary rise, reaching a second maxi- 

 mum at a very variable time but generally between the fifth and 

 seventh hours. This second maximum, however, is never so high 

 as the first. 



The second rise may be due to material absorbed from the 

 intestines being carried in the circulation to the pancreas and so 

 directly exciting the gland to activity, much in the same way a^, 

 in the case of the stomach, the absorption of digested material 

 promotes the flow of gastric juice, see § 194 ; and a similar absorp- 



