560 SCIENCE PROGRESS 



typical examples of chemical adaptations. Take, for instance, 

 the processes of digestion which occur in the duodenum. The 

 researches of von Mering and others have taught us that, from 

 half an hour to three hours after a meal, the pyloric sphincter 

 yields at intervals to admit of the passage of the highly acid 

 chyme, containing the first products of gastric digestion, into 

 the duodenum. No sooner does this acid fluid enter the gut 

 than there is an outpouring of the three juices which co-operate 

 in intestinal digestion — viz. the pancreatic juice, the bile, and the 

 succus entericus. The last named is the product of secretion 

 of the glands lining the wall of the intestine itself. Their 

 secretion might therefore be conceivably excited by the direct 

 action of the acid chyme on the mucous membrane. No doubt 

 a reflex contraction of the gall-bladder is an important factor 

 in producing the inflow of bile. If, however, we establish a 

 biliary fistula, we find that the entry of the chyme into the 

 duodenum is followed in a minute or two by an actual 

 increase in the amount of bile secreted by the liver itself. 

 Here then are two glands, the pancreas and the liver, whose 

 secreting portions are situated at some considerable distance 

 from the primary seat of the stimulus — i.e. the duodenal mucous 

 membrane. What is the nature of the connection between the 

 mucous membrane and these two glands ? A reflex secretion 

 of pancreatic juice was observed by Claude Bernard on the 

 introduction of ether into the small intestine, and was ascribed 

 by him, as well as by all later writers, to the co-operation of the 

 nervous system. The readiest means of inducing a flow of 

 pancreatic juice, apart from the administration of a meal, was 

 found by Pawlow to be the introduction of dilute hydrochloric 

 acid into the duodenum, either directly or indirectly by way of 

 the stomach. 



In 1900 it was shown independently by Wertheimer and by 

 Popielski that a secretion could be evoked by introduction of 

 acid into the duodenum or upper part of the small intestine, 

 even after section of both vagus and splanchnic nerves and 

 destruction of the spinal cord. These authors concluded, there- 

 fore, that we had here an example of a reflex action carried out 

 by the peripheral nervous system. It was to determine the 

 conditions of this peripheral reflex that Bayliss and I took up 

 the study of pancreatic secretion. We very soon found that the 

 nervous system could play very little part in the so-called reflex. 



