542 MECHANISM OF SECRETIOX 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 1 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 condition* of the formation of pepsin. — As previously men- 
tioned, Briicke 2 had noticed that the pepsin present in the gastric 
mucous membrane was not yielded entirely to one extraction, and 
Ebstein and Grtitzner 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 Griitzner 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 be 
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 oiit 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 Griitzner 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 "Leeonssur fa physiologie de la digestion," 1867, tome ii. 
- " Vorlesungen," 1874. 
3 Arch./, d. ges. Physiol., Bonn. 1874, Bd. viii. 4 Ibid., 1S77. 
5 Ibid., 1872, Bd. v.; 1873, Bd. vii. K Op. cit. 
7 " 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. 
