314 Dr. W. M. Bayliss and Prof. E. H. Starling. [Mar. 21, 



as in the splanchnics. In all his experiments, however, it was difficult 

 to exclude the possibility of the secretion having been excited by the 

 contraction of the stomach or relaxation of the pylorus, causing the 

 passage of some acid contents of the stomach into the duodenum, since 

 both these results may occur on stimulation of the vagus. We have been 

 unable to obtain secretion from stimulation of any nerves in any case 

 where this possibility was excluded, and we are inclined to believe that 

 the chemical mechanism we have described is the only method by 

 which the pancreas is awaken to secrete. The inhibition of secretion 

 obtained by some authors in an unansesthetised animal on stimulation 

 of the vagus is, we believe, a secondary phenomenon due to interference 

 with the blood supply or more probably with the flow of acid chyme 

 from the stomach, or perhaps to the rapid emptying of the upper part 

 of the gut of its acid contents. 



Secretin can be split off from its precursor in the mucous mem- 

 brane by the action of acids or boiling water. Many acids are able 

 to effect this conversion, their power being roughly proportional 

 to their ionic concentration. We have, therefore, concluded that the 

 process is one of hydrolysis. According to Fleig,* a secretin can also 

 be prepared from mucous membrane by the action of soaps, and 

 secretin has been detected in the blood flowing from the loop of 

 intestine into which oil of mustard had been introduced. Fleig 

 regards the secretin produced by the action of soaps as different from 

 that produced by the action of acids ; but it is difficult to see on what 

 grounds he makes this distinction, since the action of the secretin 

 prepared in the two ways is identical. The production of secretin by 

 the action of oil of mustard as well as the well-known secretion of 

 pancreatic juice evoked by the introduction of ether into the duodenum, 

 suggests that the hydrolytic dissociation which gives rise to secretin 

 may occur in the living cells as a result of stimulation or severe 

 lesion, since neither of these two substances will produce secretin from 

 an excised and dead mucous membrane. 



We have not yet succeeded in determining the chemical nature of 

 secretin, though we have obtained chemical evidence which will serve 

 to exclude certain classes of substances. Thus the fact that it will 

 stand boiling shows that it is neither a coagulable proteid nor a 

 ferment. It is soluble in 90 per cent, alcohol in the presence of ether, 

 but it is insoluble in absolute alcohol and ether. It is slightly diffusible 

 through animal membranes. It can be filtered through a gelatinised 

 Chamberland filter. It is not precipitated by tannic acid, thus 

 excluding bodies of alkaloid nature as well as di-amido compounds. 

 This evidence, slight though it is, points to secretin being a body of 

 relatively small molecular weight and not a colloid. It may be 

 compared to the active principle of the suprarenal glands, adrenalin, 

 * ' C. R. Soc. de Biologie,' 1903. 



