SALIVAKY GLANDS, STOMACH AND INTESTINES 747 



Physiological Evidence as to the Presence of Secretin in the Blood 

 and as to the Mode of Action of Secretin. In 1902 Wertheimer (a) (b) 

 first showed on the dog that when dilute hydrochloric acid is placed in the 

 duodenum and blood is then taken from the mesenteric vein and injected 

 into another dog the latter is stimulated to secrete pancreatic juice. 

 Wertheimer and Lepage (1902) found that ligation of the thoracic duct 

 did not prevent pancreatic secretion in a dog when dilute hydrochloric 

 acid is placed in the duodenum. Popielski considers this to favor the 

 view that the stimulation of the pancreas is not humoral, but rather a 

 reflex nervous one. Fleig confirmed these findings, but did not consider 

 them to disprove the humoral theory. Enriquez and Hallion (a) (b) 

 (1903) also showed that the injection of carotid blood from a dog stimu- 

 lated to pancreatic secretion by placing dilute hydrochloric acid in the duo- 

 denum causes a flow of pancreatic juice in the recipient, Popielski (1907) 

 confirmed the findings of Enriquez and Hallion, but considered the effect 

 upon pancreatic secretion too slight, and that the partial asphyxia brought 

 about by the anesthetic may cause the same effect. His experimental evi- 

 dence is by no means convincing. Hustin (1913) showed that electrical 

 stimulation of the duodenum or of the pancreas does not cause pancreatic 

 secretion, but that perfusion of the isolated pancreas with blood when 

 acid is in the duodenum does cause a secretion. Like Hamill and Dixon, 

 he considers the pancreas to remove the secretin from the blood. Matsuo 

 (1913) reports fairly satisfactory results in four out of eight experiments 

 by the transfusion of blood from one dog to another having dilute hydro- 

 chloric acid in the duodenum of the donor. The failures he considered 

 as due in part to cases in which the blood pressures were not the same in 

 the two dogs and, in part, to the prevention of transfusion due to coagula- 

 tion of the blood. He also confirmed Wertheimer's experiments referred 

 to above. On the whole, the evidence here is distinctly in favor of the 

 humoral theory of pancreatic stimulation. However, how is secretin 

 formed ? Is it formed in the intestinal contents by the acid chyle and 

 then absorbed, or is it formed in the duodenal wall ? The observations 

 made in attempting to answer these questions are very interesting. 

 Direct introduction of neutral secretin solutions into the duodenum does 

 not cause secretion. This has been shown by Bayliss and Starling (a) 

 (1902), Wertheimer and Dewillier (1910), Matsuo (1913), and others. 

 Very likely these negative results are due to the destructive action of pro- 

 teolytic enzymes on secretin. It is well known that both pepsin and trypsin 

 destroy it. Carlson, Lebensohn and Pearlman (1916) demonstrated this 

 for gastric juice, and others, as described previously, have demonstrated 

 its destruction by proteolytic enzymes in alkaline or neutral solutions. 

 Popielski (1907) showed that if dilute hydrochloric acid be left in the 

 duodenum for some time and this then removed and injected into another 

 animal, no stimulation is observed, He claims, however, that pancreatic 



