808 PHYSIOLOGY 



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

 better marked in the upper portions of the gut, the processes of absorp- 

 tion 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 determining 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 processes 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' experi- 

 ment on an anaesthetised animal. Better results, however, may be 

 obtained by establishing permanent fistulas. 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 con- 

 tinuity 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. In 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 now of juice from the lower 

 end, the constant emptying of the loop being provided for by the 

 peristaltic contractions of its muscular coat. 



In animals with intestinal fistulas 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 

 ten minutes. The flow remains very slight for about two hours 

 and then suddenly increases in amount during the third hour, corre- 

 sponding thus very nearly to the flow of pancreatic juice excited by 

 the same means. In this post- prandial secretion of juice it is not 

 probable that the nervous system takes any very large share, though 

 its intervention in the secretion has not been excluded by direct 

 experiment. There are certain facts which seem indeed to speak 

 for an action of the central nervous system on the processes of 

 intestinal secretion, not in the direction of augmentation, but in the 

 direction of inhibition of secretion. Thus it has been observed, on 

 many occasions, that extirpation of the nerve plexuses of the abdomen 



