CHAPTER VIII 



THE INTERNAL SECRETION OF THE INTESTINAL 



MUCOUS MEMBRANE AND THE NORMAL MECHANISM OF THE 



SECRETION OF THE PANCREATIC JUICE 



IT was first observed by Claude Bernard that the secretion of 

 the pancreatic juice is dependent on the passage of food into 

 the duodenum, and it has long been known that in the dog the 

 flow of pancreatic juice, although it begins immediately after 

 food has been taken, does not reach its maximum till either the 

 first or the second hour, but more commonly is not reached 

 until the third or fourth hour. It is to be noted that this is at 

 a time when the greatest quantity of food from the stomach 

 contents is passing into the duodenum. There has been much 

 laborious investigation and a continued keen controversy 

 as to the causal relationship existing between the passage 

 of food through the pylorus and the secretion of pancreatic 

 juice. 



It will be interesting to glance at the state of knowledge 

 on this subject in the year 1889. This can be conveniently 

 done by recalling the exposition in a standard textbook of 

 the period. M. Foster says : " Stimulation of the medulla 

 oblongata or of the spinal cord will call forth secretion in a 

 quiescent gland, or increase a secretion already going on. 

 From this we may infer the existence of a reflex mechanism, 

 though we cannot as yet trace out satisfactorily the exact path 

 of either the afferent or the efferent impulses ; all we can say is 

 that the latter do not reach the pancreas by the vagus, since 

 stimulation of the medulla is effective after the section of both 

 vagi. 



' ' A secretion already going on may be arrested by stimula- 

 tion of the central end of the vagus, and the stoppage of the 

 secretion which has been observed as occurring during and 

 after vomiting is probably brought about in this way. This 



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