INTRODUCTORY 5 



physiologists said that the nervous mechanism 

 controls the flow of the fluids ; that whenever food 

 appears in the intestine, a nervous reaction calls 

 forth the flow of bile and pancreatic juice. Bayliss 

 and Starling showed that this conception needed 

 modification. 



These investigators, in experimenting with dogs, 

 cut off all nervous connections with the small 

 intestine; yet the fluids still continued to flow into 

 it. They then suspected that possibly the acid 

 from the stomach, upon reaching the small intes- 

 tine, liberates something from the walls of the 

 organ, which "something" finds its way to the 

 pancreas and the bile, and thereby gives warning 

 of the need of these fluids. They thereupon ex- 

 tracted a piece of the intestinal wall with hydro- 

 chloric acid which is the acid found in the 

 stomach and injected this extract into the blood 

 stream. There was an immediate and copious flow 

 of pancreatic juice into the intestine. 



What then happens in the course of digestion 

 in the small intestine? The food that arrives from 

 the stomach is acid, due to the hydrochloric acid 

 that is formed in the stomach. This acid liberates 

 a substance present in an otherwise inactive state 

 in the wall of the intestine, and this substance 

 travels through the blood to the pancreas, where 

 it stimulates that organ to discharge its fluid. 



Hormones. Note that all this is performed with- 



