THE INTESTINAL HORMONE 133 



In repeating the injections of sec re tin many times 

 equal doses, he observed a conspicuous secretion 

 tfter the first dose, less after the second, still less 

 ! ter the third, till the substance rapidly became 

 [effective. Now, the introduction of acid in the 

 luodenum, however often repeated, invariably ex- 

 ites pancreatic secretion proportional to the quan- 

 Ity of acid introduced. The body evidently reacts 

 the introduction of secretin by forming an anti- 

 >ody capable of fixing it and annulling its action ; 

 tis suggests that it is not a substance normally 

 Leveloped by the body, but is an artificial extrane- 

 ms product." 



Despite this criticism, the secretin theory has 

 m very generally adopted ; to every physiologist 

 cites an experience in opposition to it, there 

 ire twenty who cite experiments that support it. 



Gastric secretin. While on the subject of diges- 

 tive juices, reference may be made to the gastric 

 juice, a fluid manufactured in the walls of the stom- 

 ach. Pavlov has conclusively shown that the flow 

 of gastric juice is unquestionably controlled by the 

 brain, since the severance of all nerve connections 

 stops the flow. This would seem to show that the 

 origin of the flow of gastric and pancreatic juices 

 is fundamentally different. However, Dr. Edkins 

 has been able to show that, in addition to a nervous 

 reflex, there is also a chemical stimulus involved. 

 His experiment followed the lines of Bayliss and 



