n EXTERNAL DIGESTIVE SECEETIONS 89 



carnivora, e.g. cat, numerous corpuscles of Pacini are seen in the 

 pancreas. 



VII. The pancreatic, like the salivary, secretion is under the 

 control of the nervous system, for it begins a few minutes after 

 the food has entered the stomach, which must be due to a nervous 

 reflex transmitted from the afferent nerves of the stomach to the 

 efferent secretory nerves of the pancreas. Experiment shows that 

 these afferent nerves are stimulated by the hydrochloric and other 

 acids directly introduced into the stomach, which after a few 

 moments produce a copious pancreatic secretion. If the exciting 

 action of these acids is abolished, by neutralising them with the 

 introduction of alkaline fluids, the secretion is considerably 

 diminished or suspended (Pawlow). The same excitatory effect 

 is obtained when neutral fats are introduced into the stomach ; 

 but it is probable that these excite pancreatic secretion by acting 

 on the afferent nerves of the duodenal mucosa ; and also because 

 part of the neutral fats that enter the stomach are split into 

 fatty acids by the lipolytic enzyme of the gastric juice (Volhard). 



These facts suggest that under normal conditions the secretion 

 of the pancreas is connected with the introduction of acid foods 

 and fluids, particularly the hydrochloric acid of the gastric juice, 

 which reflexly excites the secretory nerves of the pancreas. Direct 

 observations support this theory, and show that when gastric 

 secretion increases, the pancreatic secretion increases also. 



Subcutaneous injection of atropine diminishes the secretion of 

 pancreatic juice, but does not suspend it, as in the case of saliva. 

 Injection of pilocarpine and physostigmine produce a contrary 

 effect to atropine (Gottlieb). Pilocarpine, however, does not 

 directly excite pancreatic secretion, but it excites a profuse gastric 

 secretion. The gastric juice, in its turn, on passing into the 

 duodenum, is able, secondarily, to determine the pancreatic 

 secretion. This is proved by Launoy's observation (1904) that, if 

 the stomach be tied at the pylorus, there is no longer any secretion 

 from the pancreas after pilocarpine injection, or, at most, only a 

 few drops of a very dense secretion. 



Heidenhain showed that electrical excitation of the medulla 

 oblongata or cervical cord provoked pancreatic secretion if this 

 had been suspended, and accelerated it if the gland were already 

 functioning. Separation of the bulb from the cord by a transverse 

 section did not, however, arrest the secretion, showing that other 

 inferior centres besides that in the bulb affected the functions of 

 the pancreas. 



Besides a centre for secretory nerves, the bulb appears also to 

 contain a centre for inhibition of secretion, since, on exciting the 

 central end of the vagus, the pancreatic secretion is arrested 

 (Bernstein). This effect is probably due to a reflex vaso-con- 

 strictor action, by which the blood-supply to the gland is much 



