778 PHYSIOLOGY 



the intervention of the reflex vagal mechanism. Since it occurs 

 after cutting off the stomach from its connections with the central 

 nervous system, it must have its causation in the gastric walls them- 

 selves. That it cannot be due to mechanical stimulation is shown 

 by the fact, previously mentioned, that it is impossible by local 

 stimulation of the mucous membrane, by rubbing, or introduction of 

 sand, or any other method, to evoke a secretion. Moreover it is 

 not produced by all sorts of food. The introduction of white of 

 egg, of starch, or of bread into the stomach causes no secretion. 

 On the other hand, if bread be mixed with gastric juice and allowed 

 to digest for some time, the introduction of the semi-digested mixture 

 into the stomach evokes a secretion. We have already seen that 

 meat produces a secretion ; still more potent than meat, however, 

 is a decoction of meat, or bouillon, or Liebig's extract of meat, or 

 certain preparations of peptone. Pure albumoses and peptones 

 have no effect, so that the exciting mechanism must be some chemical 

 substances present in meat, and produced in various other foods 

 under the action of the first gastric juice secreted in response to 

 nervous stimuli. Popielski has shown that this secretion occurs 

 after complete severance of the stomach from the central nervous 

 system, as well as after destruction of the sympathetic nervous 

 plexuses of the abdomen. Since the injection of bouillon directly 

 into the circulation has no effect, this author concludes that the 

 second phase of secretion is determined by the stimulation of the 

 local nerve plexus, and that we have here, in short, a peripheral 

 reflex action, the centres of which are situated in the walls of the 

 stomach itself. There is, however, one possible explanation for this 

 second phase of secretion which was not sufficiently considered either 

 by Pawlow or by Popielski. Although the peptogenic substances, 

 those substances which evoke gastric secretion on introduction into 

 the stomach, have no effect on the gastric glands when injected 

 directly into the blood stream, it is possible that they may have 

 an influence on the cells which line the cavity of the stomach, and 

 that they may produce, in these cells, some other substance which 

 is absorbed into the blood, and acts as a specific excitant of 

 the gastric glands. A process of this nature is known to occur- 

 in the next segment of the alimentary canal, viz. the duodenum, 

 where it determines the secretion of the pancreatic juice and the 

 bile. 



Edkins has carried out a series of experiments to determine 

 whether such a chemical mechanism may not also account for the 

 secretion of gastric juice, which is excited by the introduction of 

 substances into the stomach. Edkins' experiments were carried 

 out in the following way : The animal, dog or cat, having been 



