INTESTINAL JUICE 719 



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

 suddenly increases in amount during the third hour, corresponding 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 process of intestinal secretion, not in the direction of augmenta- 

 tion, 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 or section of 

 the splanchnic nerves causes a condition of diarrhoea which may last for two or threo 

 days. This condition might be determined either by an increased motor activity of 

 the gut, or by removal of inhibitory impulses normally arriving at the intestinal glands, 

 Such a view receives support from an experiment first performed by Moreau. The 

 abdomen of a dog is opened under an anaesthetic, and three contiguous loops of small 

 intestine are separated by means of ligatures from the rest of the gut. The middle 

 loop is then denervated by destruction of all the nerve fibres lying on its blood-vessels, 

 as they course through the mesentery, care being taken not to injure the blood-vessels 

 themselves. The loops are then replaced in the abdomen and the animal left from 

 four to sixteen hours. On killing the animal at the end of this time, it is often found 

 that the middle loop, i.e. the denervated loop, is distended with fluid having all the 

 properties of ordinary intestinal juice, whereas the other two loops are empty. A 

 series of comparative experiments by Mendel and by Falloise have shown that the 

 secretion begins about four hours after the operation, increases for about twelve hours, 

 and then rapidly declines, so that at the end of two days all three loops will be found 

 empty. This has often been interpreted as due to the removal of inhibitory impulses 

 passing from the central nervous system to the local secretory mechanism, and we have 

 no direct evidence which can be adduced against such a view. It is possible, however, 

 that the hyperaamia of the gut, which is produced by the process of denervation, 

 may be sufficient to account for the increased formation of intestinal juice, since the 

 hypersemia will tend to pass off as the vessels recover a local tone. 



It is not possible to explain the flow of intestinal juice which follows a 

 meal by any assumption of nervous impulses transmitted through the local 

 nerve plexuses of the gut, since these have been divided in the making 

 of the fistula. It we exclude a nervous reflex action by the long paths, 

 namely, through the spinal cord and the sympathetic or vagus nerves, the 

 flow which attends the passage of food into the first part of the duodenum 

 must be excited by the formation of some chemical messenger. As to the 

 existence of such a chemical messenger or hormone for the intestinal secretion 

 there can be no doubt, but the evidence as to its precise nature is at present 

 conflicting. It is stated by Pawlow that the most effective stimulus to the 

 flow of succus entericus is the presence of pancreatic juice in the loop of 

 gut. No evidence has yet been brought forward that injection of pancreatic 

 juice into the blood stream will cause any flow of intestinal juice. On the 

 other hand, Delezenne and Frouin have shown that in animals provided 

 with a permanent fistula involving the duodenum or upper part of the 

 jejunum, intravenous injection of secretin always causes a secretion of 

 intestinal juice. In the upper part of the gut therefore the simultaneous 

 presence of the three juices necessary for complete duodenal digestion is 



