42 BIOLOGY AND SOCIAL PROBLEMS 



pancreas. As the food arrived in the duodenum 

 from the stomach, the contained acid was sup- 

 posed to stimulate the nerve terminals in the 

 mucous membrane of that portion of the in- 

 testine and thus to set up nerve impulses which 

 were reflected back from the central organs 

 to the gland as excitants of its activity. This 

 opinion was consonant with the fact that arti- 

 ficial stimulation of the vagus nerve was fol- 

 lowed by pancreatic secretion. But the secre- 

 tion of juice by the pancreas was subsequently 

 shown also to occur even after the nerves 

 which supply that organ, namely, the vagus 

 and the splanchnic, were cut. 



The difficulty thus introduced was removed 

 by the work of Bayliss and Starling about a 

 decade ago. They demonstrated that if some 

 of the mucous membrane of the duodenum 

 was scraped off and mixed with a weak solu- 

 tion of acid, an extract could be obtained 

 which when injected into the blood would call 

 forth an active secretion of pancreatic juice 

 even in an animal in which the nerves to the 

 pancreas had been severed. Hence they con- 

 cluded that the secretory activity of the pan- 

 creas was not necessarily dependent upon 

 nerves, but could be induced by a substance 



