542 MECHANISM OF SECRETION OF GASTRIC JUICE. 



becoming absorbed there, in some way influence the epithelium so that 

 secretion results. The exact course of this absorption is a matter of 

 some difficulty as far as the secretory epithelium is concerned, but it is 

 yet more difficult to comprehend how peptone absorbed and changed in 

 the intestinal wall should influence secretion in the stomach. If, as 

 Schiff l long ago suggested, the absorption of these products should assist 

 in building up the precursor of pepsin, we could more easily see the 

 importance of these products passing to the secreting cells. Schiff, 

 however, emphasised dextrin as being pre-eminently a " peptogenous " 

 substance. Chischin finds that it does not evoke secretion. 



The conditions of formation of the ferments of the gastric juice. 

 (a) The conditions of the formation of pepsin. As previously men- 

 tioned, Briicke 2 had noticed that th pepsin present in the gastric 

 mucous membrane was not yielded entirely to one extraction, and 

 Ebstein and Grutzner 3 pointed out that the peptic activity depended 

 considerably upon the manner in which an extract was prepared. An 

 extract made by treating the gastric mucous membrane with hydro- 

 chloric acid was much more powerful than one obtained by subjecting 

 the mucous membrane to the action of glycerin. That which was not 

 extracted by glycerin, Ebstein and Grutzner regarded as a compound 

 of pepsin with the proteid matter of the cells, this compound yielding 

 pepsin on subjection to the influence of acid, or to the action of sodium 

 chloride. Schiff 4 had also remarked, that if a dilute acid be added to 

 the stomach and left for some weeks, the extract becomes gradually 

 richer in peptic activity. Schiff accounted for this by assuming the 

 existence of a precursor of pepsin in the cells of the mucous membrane, 

 which gradually became converted into pepsin by the acid. This he 

 called propepsin. In both cases the observers were dealing undoubtedly 

 with some substance which yielded pepsin, and to this substance the 

 name pepsinogen has since been applied. Ebstein's and Griitzner's 

 test for the existence of this substance was the fact that it was not 

 dissolved by glycerin as was pepsin, and yet would yield pepsin on 

 treatment with acid. But it was soon found that there were difficulties 

 in differentiating pepsin from its precursor in this manner. Von Wittich 5 

 pointed out that when fibrin is placed in a glycerin extract of pepsin, 

 the fibrin absorbs the pepsin, and will only yield it again to fresh treat- 

 ment with acid. Ebstein and Grutzner 6 further showed that even 

 coagulated egg-albumin would do this. Thence it followed that the 

 proteids of the gastric mucous membrane might fix the pepsin, and that 

 a glycerin extract of the mucous membrane might be an extract of such 

 pepsin as was not fixed by the proteids. It was necessary, therefore, to 

 find some more definite test of the presence of pepsinogen. This was 

 supplied by Langley, 7 who found that sodium carbonate had a power- 

 fully destructive effect on pepsin, but a much less marked action on 

 certain extracts of the mucous membrane from which pepsin could be 

 derived. These extracts, therefore, were held to contain the zymogen. 

 He also inferred that the gastric glands contained the ferment in the 

 zymogen state, as they did not contain any appreciable amount of 



1 "Leconssur la physiologic de la digestion," 1867, tome ii. 

 - " Yorlesungen," 1874. 



3 Arch.f. d. ges. Physiol, Bonn, 1874, Bd. viii. 4 Ibid., 1877. 



5 Ibid., 1872, Bd. v.; 1873, Bd. vii. < ; Op. cif. 



~ "The Histology of the Mammalian Gastric Glands, and the Relation of the Pepsin 

 to the Granules of the Chief Cells," Journ. Physiol., Cambridge and London, 1882, vol. iii. 



