562 SCIENCE PROGRESS 



three sets of glands concerned in their production were aroused 

 by one and the same means — i.e. if the secretin formed by the 

 influence of acid on the mucous membrane of the duodenum 

 were a secreto-motor agent, not only for the pancreas but also 

 for the liver and the crypts of Lieberkuhn. That this is the case 

 for the liver has been shown by Bayliss and myself. In the 

 case of the intestinal secretion, the evidence is not quite so clear. 

 According to Delezenne, the intravenous injection of secretin 

 causes a flow of succus entericus, at any rate in the duodenum 

 and upper portions of the gut. On the other hand, Pawlow 

 regards mechanical distension and the presence of pancreatic 

 juice as the most effective agents in the production of succus 

 entericus, while Frouin states that secretion of this juice can be 

 excited by the injection of the juice itself, or an alkaline or 

 neutral extract of the intestinal mucous membrane into the 

 blood-stream. There is no doubt that the activity of the upper 

 part of the gut differs markedly from that of the lower. In the 

 one case, secretion predominates, in the other absorption, and 

 it is possible that the varying results obtained by different 

 observers really apply to different levels of the small intestine. 



I may mention here one other chemical excitatory process 

 in connection with the alimentary canal. Pawlow has taught 

 us to recognise two phases in the secretion of gastric juice 

 which follows the taking of a meal. The first phase of secretion 

 is presided over entirely by the central nervous system, and 

 is excited chiefly by appetite and by gustatory impressions 

 acting through the brain and the vagus nerves. The second 

 phase can be roused by the introduction of meat extracts or 

 of the primary products of gastric digestion into the stomach, 

 even after division of all its nerves. This second phase, which 

 Pawlow regarded as probably determined by local reflex 

 mechanisms, is really due, as shown by Edkins, to the ab- 

 sorption from the pyloric end of the stomach of some substance 

 or other, a gastric secretin, produced by the action of the juice- 

 arousing constituents of the food on the pyloric mucous 

 membrane. From the cells of this membrane the gastric 

 secretin is absorbed by the blood, and carried all over the 

 body, exciting, as it passes again through the walls of the 

 stomach, the activity of the glands lining the whole viscus. 



In all these examples of chemical correlation the primary 

 effect of the hormone is to excite increased activity of the 



