SECTION VII 

 THE INTESTINAL JUICE 



FOR the development of one of its most important properties, namely, that 

 of proteolysis, the pancreatic juice is dependent on the co-operation of the 

 intestinal juice or succus entericus. Besides this activating power on the 

 pancreatic juice, the intestinal juice has numerous other functions to 

 discharge in the digestion of the food-stuffs. In spite of the great similarity 

 which obtains between the microscopic structure of the wall of the gut at 

 different levels from duodenum to ileocolic valve, functionally there are many 

 differences between the upper, middle, and lower portions of the gut. 

 Speaking generally, we may say that, whereas the processes of secretion are 

 better marked in the upper portions of the gut, the processes of absorption 

 predominate in the lower sections, i.e. in the ileum. Much of the divergence 

 in the statements which have been made with regard to the factors determin- 

 ing secretion and absorption in the small intestine is due to the failure to 

 appreciate this great difference between the activity of the mucous membrane 

 at various levels. 



The process of secretion in the small intestine may be studied by isolating loops by 

 means of ligatures, and determining the amount of secretion formed in these loops in 

 the course of a few hours' experiment on an anaesthetised animal. Better results, 

 however, may be obtained by establishing permanent fistulae. These fistulas are of 

 two kinds. Thiry's original method of establishing a fistula consisted in cutting out 

 a loop of intestine, and restoring the continuity of the gut by suturing the two ends 

 from which the loop had been severed. The upper end of the loop itself is closed and 

 the lower end is sutured into the abdominal wound. For some purposes it is better 

 to make a Thiry-Vella fistula. lit this case the continuity of the gut is restored as in 

 the simple Thiry fistula, but both ends of the excised loop are left open and brought 

 into the abdominal wound. In such a fistula it is easy to introduce substances into 

 the upper end and determine the flow of juice from the lower end, the constant empty- 

 ing of the loop being provided for by the peristaltic contractions of its muscular coat. 



In animals with intestinal fistulae a number of different conditions have 

 been found to give rise to a flow of succus entericus, and so far no qualitative 

 difference has been recorded between the upper and lower ends of the gut. 

 A condition which will cause a free flow of juice from a fistula high up in the 

 intestine will generally cause a scanty flow from a fistula made from the 

 ileum. In all cases it is found that a flow of juice is produced in consequence 

 of a meal. If a dog with a fistula, which has been starved for twenty-four 

 hours, be, given a meal of meat, a flow of juice may begin within the next 



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