544 MECHANISM OF SECRETION OF GASTRIC JUICE. 
described till some years later. Langiey 1 showed that the method of 
separating pepsin from pepsinogen was applicable also to the remain, 
since rennet-ferment was destroyed by sodium carbonate, whilst rennet- 
zyniogen is affected much less powerfully. Hammarsten has also shown 
that the amount of rennet-ferment that can be extracted from the 
cardiac end of the stomach is proportionally much greater than that 
obtainable from the pyloric mucous membrane. Grutzner 2 has shown 
that in the gastric glands of the dog, the rennet-ferment diminishes in 
amount during digestion, and that the amount of diminution runs 
parallel to that of pepsin. It seems that where pepsin is greatest m 
quantity, there also is rennet-ferment most abundant, and it seems 
probable that the granules of the chief cells contain the zymogens both 
of rennet-ferment and pepsin. We cannot say whether the granules are of 
one kind or whether there are separate forms of granules for the separate 
ferments. But though in general the zymogen of the rennet-ferment, 
and not the actual ferment, is existent in the gastric cells, yet in 
some cases, e.g. the calf and sheep, the zymogen is presumably in a 
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 
Fig. 44.- — The figures at the abscissa on the base line refer to the 
number of hours elapsed since the last meal. The length of the 
ordinates indicates the amount of pepsin yielded at any time. F is 
the record of variation in the fundus mucous membrane, P of 
variation in the pyloric mucous membrane. — After Grutzner. 
much less stable condition, for a watery extract of the stomach of 
these animals yields rennet-ferment in large quantities. As regards 
the differentiation of the rennet-ferment from the proteolytic, they can 
be separated from one another by chemical means, although we have 
no morphological signs of their distinction. Hammarsten's method of 
separating the two ferments chemically depends upon the fact that 
the gradual addition of lead acetate precipitates the pepsin sooner than 
the rennin. 3 
The variations in the amount and composition of gastric juice 
during the course of digestion. — The amount of pepsin that can be 
extracted from the mucous membrane has been estimated by Grutzner. 4 
He compared concurrently that obtained from the fundus with that 
yielded by the pyloric region. In the above chart (Fig. 44), which shows 
the chief variation during the lapse of some hours after a meal, the most 
1 "On the Destruction of the Ferments of the Alimentary Canal," Journ. Physiol., 
Cambridge and London, 1882, vol. iii. 
2 Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvi. 
The conditions of formation of the hydrochloric acid of the gastric juice are treated 
of in a preceding article (see pp. 351 et seq.). 
4 Arch./, d. ges. Physio/., Bonn, 1S79, Bd. xx. 
