ii EXTERNAL DIGESTIVE SECRETIONS 109 



that when the animal fed the alimentary bolus dropped out 

 through the oesophageal fistula. For food to reach the stomach it 

 was necessary to introduce it either through the lower orifice of 

 the oesophageal fistula or through the gastric fistula. 



When an animal thus prepared was made to masticate and 

 swallow food that dropped out again through the oesophageal 

 fistula (sham or imaginary feeding), a marked secretion of gastric 

 juice (psychical secretion} was invariably noted 5-6 minutes later. 

 On section of the vagi (the right below the point at which the 

 cardiac branches and the inferior laryngeal are given off, and the 

 left at the neck) this reflex secretion ceased entirely. On exciting 

 the peripheral trunk of the left vagus with two induction shocks 

 per sec. the flow through the fistula reappeared. 



These results, which were constant under the given con- 

 ditions, contradicted the previous negative results of vagus 

 .excitation obtained under other experimental conditions by many 

 physiologists, Heidenhain included. They prove beyond doubt 

 that the centrifugal nerves that regulate the gastric secretion are 

 contained in the trunk of the vagus. 



Von Mering (1899) showed that atropine and pilocarpine pro- 

 duce similar effects on gastric secretion to those which Heidenhain 

 obtained on salivary secretion : the former diminishes or suspends 

 secretion of gastric juice, the latter increases it even fourfold. 

 These effects can only be explained by admitting that atropine 

 has a paralysing, and pilocarpine an exciting, action on the 

 secretory fibres contained in the vagus. 



Other facts, however, show that the gastric secretion does not 

 depend exclusively upon the secretory fibres of the vagus, since 

 the stomach is capable of sufficiently digesting the alimentary 

 substances introduced into it, even when the vagi have been 

 divided. This suggests that other secretory fibres, spinal or 

 sympathetic in origin, influence the gastric glands: but there are 

 at present no experimental proofs of this conjecture. Experiments 

 made with this object (section of splanchnic, excision of caeliac 

 plexus) have given negative results. Heidenhain assumed that 

 the digestive capacity of the stomach persists after division of the 

 centres of all cranial and spinal nerves to the stomach. It is 

 probable (although it has not been experimentally demonstrated) 

 that the gangliar plexuses in the walls of the stomach represent a 

 system capable of special reflex activation of secretion. 



The stimuli that normally determine gastric secretion by reflex 

 paths are the food -stuffs, which excite the nerves of taste and 

 other centripetal nerves to the mucous membrane of the mouth, 

 pharynx, oesophagus and stomach. The fine experiments of 

 Pawlow and his collaborators (1889-97) have established as an 

 indispensable condition of the production of a flow of gastric juice 

 by the aliments introduced through the mouth, that the animal 



