90 PHYSIOLOGY CHAP. 



diminished. The same result is obtained on stimulating other 

 sensory nerves, so as to excite nausea or vomiting. 



Pawlow's subsequent work on dogs established beyond a doubt 

 that the secretory nerves of the pancreas run in the vagus. If in 

 a dog one vagus be divided in the cervical region, and the bulb 

 separated from the cord after 3 to 4 days by incision, artificial 

 respiration being given, and a pancreatic fistula established, 

 any stimulation of the peripheral end of the vagus by strong or 

 weak induced currents produces pancreatic secretion. Previous 

 researches carried out without these precautions had always led 

 to a negative result, owing to the great sensibility of the gland to 

 all influences capable of altering its blood-supply. 



The vagus is not, however, the only nerve which contains 

 secretory fibres to the pancreas. According to Kudrewetzsky, 

 the splanchnic also supplies some, although their secretory action 

 is much less developed than that of the vagus. 



A recent theory of Bayliss and Starling as to the mechanism 

 of secretion, whether of the pancreas or of other glands in the 

 digestive tube, has been very generally accepted. 



According to these authors there is, besides the nervous con- 

 trol which is able in itself to excite pancreatic secretion, another 

 secretory mechanism, which acts independently of the nervous 

 system. This consists in an internal secretion by the mucous 

 membrane of the duodenum, of a special substance (secretin} 

 which, on entering the circulation, travels with the blood to the 

 pancreatic cells, exciting them directly and causing secretion. 



Their theory rests particularly upon the fact that, on macerating 

 the mucous membrane of the intestine (especially of the duodenum 

 and adjacent parts) in a solution of hydrochloric acid, a solution 

 is obtained on filtering, which, when injected into the veins, 

 produces a profuse pancreatic secretion. 



This fact has been controlled by many, and invariably con- 

 firmed ; but it does not seem to us to justify the theory that has 

 been based upon it. To say that secretin thus artificially prepared 

 is able to excite secretion in the pancreas and many other glands 

 does not mean that it is elaborated and circulated under normal 

 conditions of the duodenum. We know from an observation of 

 U. Lombroso (1903) that such is not really the case. In dogs 

 with a Pawlow's pancreatic fistula the secretion diminishes, and 

 ceases entirely after some days, if the papilla of the duct be 

 destroyed, even if the secretory ducts are still open. 



The same occurs if, instead of establishing a pancreatic fistula 

 by Pawlow's method, it is prepared in Cl. Bernard's way, which 

 does not respect the integrity of the duct or the papilla. Why, 

 in all these cases, if the secretory mechanism of the pancreas 

 consisted (as on the hormone theory of Bayliss and Starling) in 

 the production of secretin during the passage of the gastric 



