288 CHEMICAL MECHANISMS OF SECRETION 



and that the substance so secreted might travel in the blood- stream 

 to the pancreatic cells and set them in activity. 



This view did occur to Bayliss and Starling, who, on testing 

 it experimentally, found it to be the correct one, and so not only 

 brilliantly supplemented the work of the St. Petersburg school 

 on pancreatic secretion, but made a new departure in our know- 

 ledge regarding secretory processes, and opened up a new field 

 to research. 



THE CHEMICAL MECHANISMS OF SECRETION CHEMICAL 

 EXCITANTS OP SECRETION OR HORMONES. 



Pancreatic Secretion and Secretin. The apparently local char- 

 acter of the reaction when acid was placed in the intestine, described 

 in the preceding section, led Bayliss and Starling to experimenta- 

 tion upon the subject, from the view that there might here be 

 an extension of the local reflexes, the action of which in movements 

 of the intestinal wall these observers had already investigated. It 

 was soon found, however, that the phenomenon was one of an 

 entirely different order, and that the secretion of the pancreas 

 is normally called into action not by nervous agency at all, but 

 by a chemical substance formed in the mucous membrane of the 

 upper parts of the small intestine under the influence of acid, 

 and carried thence by the blood-stream to the gland cells of the 

 pancreas. To the active substance the name secretin has been 

 given by the authors. 



In the earlier experiments of Bayliss and Starling, dogs were 

 used, but in a later research other animals were employed (rabbit, 

 cat, and monkey), and it was demonstrated that the reaction is a 

 general one for all vertebrates. 



The animals received an injection of morphia previous to the 

 experiment, and during its course were anaesthetised with A.C.E. 

 mixture. In order to keep the condition of the animals constant 

 during the experiment, artificial respiration was resorted to, and 

 a constant depth of anaesthesia was attained by placing the 

 anaesthetising bottle in the air circuit ; this procedure is especially 

 necessary when the vagi have been cut. The animals in the earlier 

 experiments had not been fed for a period of eighteen to twenty- 

 four hours, but in later experiments it was shown that secretin 

 is active no matter what may be the state of digestion. In order 



