SALIVAEY GLANDS, STOMACH AND INTESTINES 745 



kinase in activating trypsinogen. This observation suggests a ferment 

 action but, on the other hand, they observed the relation between secretin 

 and pancreas to be a quantitative one and not a catalytic one. 



Specific Chemical Character of Secretin. Is duodenal secretin the 

 same as or different from gastrin, histamin or vasodilatin in chemical 

 characteristics ? The chemical properties of gastrin have already been 

 discussed and the studies thereon suggest that it is not identical with duo- 

 denal secretin. The most specific studies on duodenal secretin show that 

 it is very easily oxidized, easily destroyed by bacteria, acids, bases, and by 

 proteolytic enzymes. Certainly, no such labile character can be ascribed 

 to gastrin. 



Is secretin identical with histamin ? The fact that fair evidence has 

 been obtained, indicating the presence of histamin in duodenal mucous 

 membrane, has led some to conclude that histamin is identical with secretin 

 and that it is the vasodilatin of Popielski. Thus Barger and Dale (1911) 

 separated from 'duodenal mucosa a picrat "quite similar to histamin 

 picrat," with a melting point of 232 C. The product gave all the 

 physiological reactions of histamin and the authors suggest that it prob- 

 ably is a constituent of Popielski' s vasodilatin, but that it is not neces- 

 sarily identical with duodenal secretin. Mellanby and Twort (1912) 

 found organisms which form histamin from histidin in the intestinal con- 

 tents from the duodenum downward in the guinea, pig, and consider the 

 origin of histamin in the intestinal wall, as due to the action of these 

 organisms. Berthelot and Bertrand (1912) also isolated an organism 

 from the human intestine which produces histamin from histidin. Re- 

 cently Abel and Kubota (1919) from their studies conclude that histamin 

 may be obtained from many tissues and, in fact, consider it to be one of the 

 building stones in proteins because they obtained evidence of its formation 

 in the acid hydrolysis of casein and edestin. Their evidence is in part 

 chemical and in part biological, and they conclude that the motilines, vaso- 

 dilatin and "histamin-like" substances in tissues are all one and the same 

 substance histamin. Their work has not been confirmed thus far. Even 

 if histamin is obtained by extracting the tissue in question, and even 

 though histamin does possess the secretagogue and other physiological 

 properties attributed to gastrin and secretin, the all important fact remains 

 that the secretin activity from duodenal mucous membrane, although it 

 appears to give many of the color and precipitation reactions of histamin, 

 still appears to be very much less stable. 



Are secretin and vasodilatin identical chemically? It will be re- 

 membered that Bayliss and Starling tried to prepare their secretin free 

 from depressor action. The general impression seems to be that they 

 succeeded, but a careful examination of their tracings showing the blood 

 pressure and secretory effects reveals that with lowering of the depressor 

 action in their extracts they also lowered the secretagogue activity very 



