116 THE WORK OF THE DIGESTIVE GLANDS. 



observes a diminution of the normal secretion a diminution which often 

 lasts for a long time. I give here one experiment as an example : 

 The secretion was recorded every five minutes. 



5-6 c.c. 

 6-6 

 7-2 

 7-4 

 7-2 

 6-8 



Of the dog's own pancreatic 



juice 70 c.c. were here poured 



into the stomach. 



5'6 c.c. 



2'2 . 



1-4 c.c. 



1-0 



1-0 



1-1 



1-5 



1-6 



5-0 



6-8 



6-0 



5'7 , and so on. 



We see in the above an instructive instance of how the work of one 

 segment of the alimentary canal is connected with and dependent upon 

 that of the previous one. Thus, the saliva which moistens everything 

 dry, is able to act as an exciter of gastric secretion by virtue of its 

 content of water. In the stomach itself it is in this way ensured, that 

 the psychic secretion which is the forerunner of digestion is continued 

 by the influence of the saliva. The acid of the gastric juice acts in its 

 turn as an excitant of the pancreatic gland, and thus the mutual 

 influence which the digestive glands exert upon each other is clearly 

 manifested. 



We are, therefore, justified in saying that the acid is a specific exciter 

 of tbe pancreatic gland. Where, however, is its point of action ? 

 There are two possibilities. The acid works either locally by 

 exciting the peripheral end-apparatus of the centripetal nerves in the 

 mucous membrane, or else it is absorbed into the blood and stimu- 

 lates either the secretory centre or the gland cells directly. If we 

 analyse the facts already communicated, together with the results of 

 some new experiments, we must decidedly accept the first hypothesis.* 

 Let us attentively consider the facts of the acid effect. The question as 

 to how these substances could act in the blood is very simple, namely, 

 by reducing its alkalinity. If, therefore, pancreatic juice is expelled, as 

 soon as acids are introduced from without, the alkalinity of the blood 

 must thereby be reduced, and this can be the only alteration which 



* Bayliss and Starling have recently shown (Proceedings Royal Society, London, 

 vol. Ixix. 1902, p. 352, also CntralMatt f. Physiologic, Bd. xv. 1902, p. 682) that 

 the exciting agency is not the acid itself, but a substance produced by its action 

 upon the mucous membrane of the duodenum and of the upper jejunum. This 

 substance, which they term "seeretin" is effective when injected into the blood 

 stream, after extirpation of the solar plexus and destruction of all nervous fila- 

 ments passing to the isolated loop of intestine, also after the injection of atropin. 

 Hence the) 1 conclude that its action is not a reflex one through nervous channels. 

 The substance is not destroyed by boiling or neutralisation of the acid extract of 



