708 PHYSIOLOGY 



of this proceeding Heidenhain and Pawlow independently devised another method 

 to enable us to determine the causes of pancreatic secretion. The pancreas in most 

 cases possesses two ducts, the upper one opening along with the bile duct, the lower one 

 a short way down. The relative sizes of these two ducts vary in different animals, 

 the lower one being larger in the dog, while in man and the cat the upper one is larger. 

 In order to establish a pancreatic fistula in a dog, a small quadrilateral piece of the 

 duodenal wall is exsected, having the papilla of the lower duct opening in the middle 

 of its mucous surface. The integrity of the gut is restored by suturing in a single line 

 of stitches the margins of the wound in the duodenum, and the exsected piece is brought 

 to the surface and stitched in the middle of the abdominal wound. The greater part 

 of the pancreatic secretion will escape by the fistula, and can be collected either by the 

 insertion of a cannula into the duct or by attaching a glass funnel below its orifice. 

 Great care has to be taken in the after treatment of such animals. The pancreatic 

 juice, which flows over the papilla, acquires in so doing strong proteolytic powers, 

 and tends therefore to dissolve and irritate the adjacent abdominal wall. This can be 

 prevented by taking care to collect all the juice, and to allow none to flow away over 

 the surface of the body. Another drawback is that the continual loss of pancreatic 

 juice in many cases seriously affects the animal's health. This may be obviated to a 

 certain extent by keeping the animal on a milk diet with the addition of sodium bicar- 

 bonate to replace the loss of this salt by the juice. With great care Pawlow has succeeded 

 in keeping such animals in a perfectly healthy condition. 



In the fasting condition there is, as a rule, no secretion of juice, though the 

 escape of a few drops may be observed at long intervals. If a meal be 

 administered to the animal, a flow of juice begins in one to one and a half 

 minutes. From this time there is a steady, slow rise of the rate of secretion, 

 which lasts for two to three hours, and then gradually diminishes. The 

 greatest increase in flow is observed at the time when the first portions of 

 digested food escape from the stomach into the duodenum. The secretion 

 must therefore be determined in some way by the entry of this food into the 

 duodenum. By experiments on dogs possessing a gastric as well as a 

 pancreatic fistula, it has been shown that the introduction of acid, e.g. 0-4 per 

 cent. HC1, into the stomach evokes, as soon as it passes into the duodenum, 

 a rapid flow of pancreatic juice. A similar, but smaller, effect is produced by 

 the passage of oil from the stomach into the duodenum. The introduction 

 of alkalies is without effect. Weak acids are also effective exciters of 

 secretion if they be introduced directly into the duodenum itself or into a loop 

 of small intestine. The effect gradually diminishes as the loop which is 

 chosen comes nearer to the caecum, and as a rule the injection of dilute acid 

 into the lower foot or eighteen inches of ileum is without effect on the 

 pancreas. The striking resemblance between the secretion thus evoked and 

 that produced in the salivary glands by injection of acid into the mouth 

 suggests that we have here to do with a reflex of the same kind as that which 

 affects the salivary glands. In the search for the channels of this reflex 

 Heidenhain showed that stimulation of the medulla oblongata occasionally 

 produced a flow of pancreatic juice. He was unable, however, to obtain any 

 secretion on stimulation of the vagus nerve. The pancreas receives fibres 

 from the vagi as well as from the splanchnic nerves (sympathetic system). 

 According to Pawlow the ill success of Heidenhain's experiments was due to 

 the fact that in any operation a gland is played upon by reflex impulses 



