SECRETIN AND CHOLIN 39 



the physiological influence and significance of which have 

 elsewhere (Vol. I of this series, Chemistry of the Tissues > 

 pp. 185-190) been detailed. Secretin cannot, however, be 

 identified as cholin, the activities of the two sub- 

 stances being in no wise parallel ; the secretory effect of cholin 

 (but not of secretin) being completely eliminated by atropin. 

 "Secretin" is, however, apparently not a simple substance, 

 but is perhaps a mixture of a number of agents capable of 

 exciting secretory activity, in the group of which cholin 

 doubtless is included. Keeping in mind the fact that cholin 

 is an exceedingly labile substance, subject to marked changes 

 from comparatively simple disturbances (as seen, for in- 

 stance, in its transformation into neurin, muscarin and 

 acetylcholin) and to functional exaggerations (cf. Vol. I, p. 

 189, of this series, The Chemistry of the Tissues), it is 

 not easy to get rid of the idea that perhaps secretin is nothing 

 more than a mixture of cholin and of its transformation 

 products. Of course this is no more than an unproved con- 

 jecture, which it is true would serve to bring secretin and 

 the "vasodilatins" (probably closely related to cholin) 

 under a common heading. 



As previously indicated, cholin is one of the general 

 tissue constituents ; and from the investigations of Popiel- 

 ski J1 and his students "vasodilatins" can doubtless be ex- 

 tracted from practically all tissues. These are powerful 

 substances capable, when injected intravenously with proper 

 precautions, of inducing fall of blood-pressure, secretion of 

 saliva, of gastric, intestinal and pancreatic fluids, increase of 

 peristalsis, spasms, loss of haemic coagulability and in- 

 creased flow of the lymph. Popielski believes that a relative 

 anaemia, dependent upon the lowered blood-pressure, and 

 consecutive irritation of the nervous centres are fundamen- 



11 L. Popielski (Lemberg), Centralbl. f. Physiol., 16, 505, 1902; 19, 801, 

 1906; Pfltiger's Arch., 120, 451, 1907; 121, 239, 1908; 126, 483, 1909; 128, 

 191, 223, 1909. 



